Cd34+,cd45- placental stem cell-enriched cell populations

ABSTRACT

Provided herein are methods and compositions for the production of hepatocytes from placenta stem cells. Further provided herein is the use of such hepatocytes in the treatment of, and intervention in, for example, trauma, inflammation, and degenerative disorders of the liver. Also provided herein are compositions and methods relating to combinations of nanofibrous scaffolds and adherent placental stem cells and methods of using the same in cartilage repair. Finally, provided herein are compositions and methods relating to nonadherent, CD34 + CD45 −  stem cells from placenta.

This application claims benefit of U.S. Provisional Application No.60/901,066, filed Feb. 12, 2007; U.S. Provisional Application No.60/901,076, filed Feb. 12, 2007; U.S. Provisional Application No.60/905,664, filed Mar. 7, 2007; U.S. Provisional Application No.60/906,064, filed Mar. 8, 2007; and U.S. Provisional Application No.60/966,577, filed Aug. 28, 2007, the disclosures of each of which areincorporated herein in its entirety.

1. FIELD

Provided herein are methods and compositions relating to stem cells fromplacenta. Provided herein are methods for the production of hepatocytesfrom human adherent placental stem cells, and the use of suchhepatocytes in the treatment of, and intervention in, for example,trauma, inflammatory and degenerative disorders of the liver. Alsoprovided herein are compositions and methods relating to combinations ofnanofibrous scaffolds and adherent placental stem cells and methods ofusing the same in cartilage repair. Finally, provided herein arecompositions and methods relating to nonadherent, CD34⁺CD45⁻ stem cellsfrom placenta.

2. BACKGROUND

Somatic stem cells have been proposed for various therapeuticapplications, including, for example, in animal models of cellreplenishment therapy. The therapeutic potential of grafted stem cellscan only be translated to clinical use if an ethically acceptable sourceof autologous stem cells is available, and if control of self renewaland fate decisions that program stem cell maturation into specific celltypes is achieved.

A number of studies have described differentiation of embryonic stemcells down the hepatocyte lineage (see, e.g., Sharma, N. S. et al.,Biotechnology & Bioengineering, 94 (6): 1053-93 (2006); Maguire, T., etal, Biotechnology & Bioengineering, 93(3):581-591 (2006) and Chen Y, etal., Cell Transplant. 2006; 15(10):865-71). In addition, human bonemarrow derived mesenchymal cells were examined for the capacity todifferentiate into functioning hepatocytes with some success (Ong S Y,Dai H, Leong K W, Tissue Eng. 2006 Oct. 1; Ong S Y, Dai H, Leong K WBiomaterials (22):4087-97 (2006)(epub Apr. 17, 2006); Sato Y, Araki I I,Kato J, Nakamura K, Blood. 106(2):756-63 (2005) (epub Apr. 7, 2005).

Hepatic disorders increasingly account for significant morbidity andmortality. Destruction of liver function by environmental and pathogeniccauses presents significant public health risks to otherwise healthyindividuals. Replacement of damaged or killed hepatocytes in suchdamaged organs is therefore a significant clinical goal. However, anethically acceptable source for stem cells that can differentiate intohepatocytes remains unavailable. These and other unmet needs areprovided herein.

3. SUMMARY

In one aspect, provided herein are methods and compositions for theproduction of hepatocytes from adherent placental stem cells, andmethods of using such hepatocytes to treat diseases, disorders orconditions, such as those involving trauma, inflammation, or systemicdisorders of the liver, e.g., diseases, disorders or conditionsassociated with hepatic inflammation. In one embodiment, provided hereinis a method of producing a hepatocyte, comprising culturing a placentalstem cell under conditions and for a time sufficient for said stem cellto exhibit a characteristic of a hepatocyte. In a specific embodiment,said characteristic is the production of albumin or expression of a geneencoding albumin. In another specific embodiment, said characteristic isthe production of urea. In another specific embodiment, said culturingcomprises contacting said stem cell with sodium butyrate. In anotherspecific embodiment, said culturing comprises encapsulating said stemcell in alginate-poly-L-lysine. In another embodiment, provided hereinis a hepatocyte produced by differentiation of a placenta-derived stemcell. Also provided herein is a method of treating a subject having adisease, disorder or condition associated with abnormal liver function,comprising introducing such a hepatocyte into said subject. In a morespecific embodiment, the disease, disorder or condition is cirrhosis ofthe liver. In certain embodiments, the disease or conditions resultsfrom liver toxicity caused by, e.g., alcohol or ingestion of toxins suchas, e.g., mushroom toxins. In certain embodiments, the disease orcondition is a viral infection, e.g., a hepatitis A, B, C, D, or Einfection. In certain embodiments, the disease or condition is fulminantor subfulminant hepatitis. In another aspect, provided herein is amethod for determining whether a compound has liver toxicity activity,comprising contacting a hepatocyte produced by differentiation of aplacenta-derived stem cell with the compound, and determining whetherthe compound is toxic to the hepatocytes.

In another embodiment, the placental stem cell is positive forcytokeratin 18. In another embodiment, provided herein is a populationof placental stem cells, or cells differentiated therefrom, at least50%, 70%, 80%, 90%, 95% or 99% of which are positive for cytokeratin 18.In another embodiment, provided herein is a population of cellscomprising placental stem cells, or cells differentiated therefrom,wherein at least 50%, 70%, 80%, 90%, 95% or 99% of the placental stemcells or cells differentiated therefrom are positive for cytokeratin 18.In another embodiment, the invention provides a method of isolating aplacental stem cell, or population of placental stem cells, or cellsdifferentiated therefrom, comprising selecting a cytokeratin 18⁺placental stem cell, or cytokeratin 18⁺ placental stem cells, andisolating said stem cell or stem cells from other placental cells.

In another aspect, provided herein is a composition comprising aplurality of cells encapsulated in alginate, wherein said cells aredifferentiated from placental stem cells. In one embodiment, said cellsexpress at least one marker of a hepatocyte not expressed by, orexpressed to a detectably different degree than, a placental stem cell.In another embodiment, said alginate is in the form of beads. In aspecific embodiment, said beads are from about 200 μm to about 800 μm insize. In another specific embodiment, said beads average about 500 μm insize.

In another aspect, provided herein is a mouse comprising human placentalstem cell-derived hepatocytes or hepatogenic cells, wherein said mouseis produced by a method comprising the steps of: (a) irradiating saidmouse with gamma radiation sufficient to kill substantially all of theendogenous bone marrow cells; (b) administering to said mouse sufficientbone marrow or bone marrow-derived cells from a NOD/SCID mouse toreconstitute the hematopoietic system of the mouse; and (c)transplanting to said mouse a plurality of hepatocytes or hepatogeniccells, wherein said hepatocytes or hepatogenic cells are differentiatedfrom a plurality of CD10⁺, CD34⁻, CD105⁺, CD117⁻, CD200⁺ placental stemcells. In one embodiment, said placental stem cell is additionallycytokeratin 18⁺ and negative for at least one other cytokeratinexpressed by differentiated hepatocytes. In another embodiment, saidhepatocytes or hepatogenic cells are administered into an ear pinna ofthe mouse. In another embodiment, said hepatocytes or hepatogenic cellsare infected with a virus. In a specific embodiment, said virus ishepatitis A virus, hepatitis B virus, hepatitis C virus, hepatitis Dvirus, or hepatitis E virus. In a more specific embodiment, the virus ishepatitis B virus.

In another aspect, provided herein is a method of identifying anantiviral agent, comprising contacting a mouse with a compound ofinterest, wherein serum from said mouse has detectable levels of virus,and wherein said compound is an antiviral agent if said contactingresults in a detectable reduction in the amount of said virus in serumfrom said mouse, compared to serum from said mouse not contacted withthe compound of interest, and wherein the mouse is produced by a methodcomprising the steps of: a. irradiating said mouse with gamma radiationsufficient to kill substantially all of the endogenous bone marrowcells; b. administering to said mouse sufficient bone marrow or bonemarrow-derived cells from a NOD/SCID mouse to reconstitute thehematopoietic system of the mouse; and c. transplanting to said mouse aplurality of hepatocytes or hepatogenic cells, wherein said hepatocytesor hepatogenic cells are differentiated from a plurality of CD10⁺,CD34⁻, CD105⁺, CD117⁺, CD200⁺ placental stem cells. In one embodiment ofthe method, said virus is hepatitis A virus, hepatitis B virus,hepatitis C virus, hepatitis D virus, or hepatitis E virus. In specificembodiments of the method, an antigen or a nucleic acid of said virus isdetected. In a more specific embodiment, said virus is hepatitis Bvirus. In a specific embodiment of the method, wherein a viral antigenis detected, said antigen is HBeAg or HBsAg. In another specificembodiment, wherein a viral nucleic acid is detected, said nucleic acidis the covalently closed circular form of hepatitis B virus. In a morespecific embodiment, said nucleic acid is detected by PCR using primersspecific for the covalently closed circular form of hepatitis B virus.

In another aspect, provided herein is a matrix, and compositionscomprising such a matrix, wherein the matrix comprises placental stemcells that have differentiated to a hepatogenic or chondrogenic lineage,or to hepatocytes or chondrocytes. In a more specific embodiment, saidmatrix is a three-dimensional scaffold. In another more specificembodiment, said matrix comprises collagen, gelatin, laminin,fibronectin, pectin, ornithine, or vitronectin. In another more specificembodiment, said matrix is, or comprises, a nanofibrous scaffold, e.g.,an electrospun nanofibrous scaffold. In a more specific embodiment, saidnanofibrous scaffold comprises poly(L-lactic acid) (PLLA), type Icollagen, a copolymer of vinylidene fluoride and trifluoroethylnee(PVDF-TrFE), poly(-caprolactone), poly(L-lactide-co-ε-caprolactone)[P(LLA-CL)] (e.g., 75:25), and/or a copolymer ofpoly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and type I collagen.In another more specific embodiment, said electrospun nanofibrousscaffold promotes the differentiation of placental stem cells intochondrocytes or hepatocytes. In another specific embodiment, theelectrospun nanofibrous matrix or scaffold comprises placental stemcells that have differentiated into chondrocytic cells and/orchondrocytes, or into hepatocytic cells and/or hepatocytes. In anothermore specific embodiment, the matrix is an amniotic membrane or anamniotic membrane-derived biomaterial. In another more specificembodiment, said matrix comprises an extracellular membrane protein. Inanother more specific embodiment, said matrix comprises a syntheticcompound. In another more specific embodiment, said matrix comprises abioactive compound. In another more specific embodiment, said bioactivecompound is a growth factor, cytokine, antibody, or organic molecule ofless than 5,000 daltons.

In another embodiment, provided herein is a composition comprisingisolated adherent CD10⁺, CD34⁻, CD105⁺, CD200⁺ placental stem cells andan electrospun nanofibrous scaffold. In a specific embodiment, saidnanofibrous scaffold comprises fibers of poly(L-lactic acid) (PLLA),poly lactic glycolic acid (PLGA), type I collagen, a copolymer ofvinylidene fluoride and trifluoroethylnee (PVDF-TrFE),poly(-caprolactone), poly(L-lactide-co-ε-caprolactone) [P(LLA-CL)](e.g., 75:25), and/or a copolymer ofpoly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and type I collagen.In another specific embodiment, said nanofibrous scaffold comprisesfibers that average between about 250 nanometers and about 10 μm inthickness. In another specific embodiment, said composition is contactedwith conditions in which the placental stem cells differentiate intochondrogenic cells or chondrocytes. In another embodiment, providedherein is a method of making a composition comprising contactingadherent CD10⁺, CD34⁻, CD105⁺, CD200⁺ placental stem cells with anelectrospun nanofibrous scaffold, wherein said nanofibrous scaffold ismade by electrospinning PLLA or PLGA at about 20 kV at about 30 cmneedle to collector distance and about 0.05 mL/min. to about 0.1 mL/minflow rate, wherein said PLLA or PLGA are in solution at about 10% w/w toabout 20% w/w.

In another aspect, provided herein is an isolated placental stem cellthat is CD34⁺ and CD45⁻. In a specific embodiment, said CD34⁺, CD45⁻stem cell is hematopoietic. In another specific embodiment, said CD34⁺,CD45⁻ stem cell is non-adherent when cultured on a tissue culturesurface, e.g., plastic. In a specific embodiment, provided herein is anisolated cell population enriched in placental stem cells that are CD34⁺and CD45⁻. In specific embodiments, at least 50%, 70%, 90% or 95% ofcells in said population are CD34⁺CD45⁻ placental stem cells. In anotherspecific embodiment, the isolated cell population comprisesproportionately more CD34⁺ and CD45⁻ placental stem cells than placentalperfusate (e.g., perfusate from perfusion of a placenta with 750 mL 0.9%saline solution). In another specific embodiment, the isolated cellpopulation comprises a stem cell that is not CD34⁺ and CD45⁻. In a morespecific embodiment, said stem cell that is not CD34⁺ and CD45⁻ is aCD34⁻ adherent placental stem cell. In a more specific embodiment, saidadherent placental stem cell is CD200⁺, CD105⁺, CD90⁺, CD10⁺, CD34⁻and/or CD45. In another specific embodiment, said stem cell that is notCD34⁺ and CD45⁻ is a bone marrow-derived mesenchymal stem cell. Inanother specific embodiment, said stem cell that is not CD34⁺ and CD45⁻is a CD34⁺, CD45⁺ hematopoietic stem cell. In another specificembodiment, said stem cell that is not CD34⁺ and CD45⁺ is containedwithin cord blood or placental blood.

In another specific embodiment, the isolated cell population is aplurality of total nucleated cells (TNC) from placental perfusate. In aspecific embodiment, the TNC from placental perfusate comprisesplacental cells from at least, or at most, 50, 100, 150, 200, 250, 300,350, 400, 450 or 500 mL placental perfusate. In another specificembodiment, the TNC from placental perfusate have been treated to removeat least one type of non-red blood cell.

In another embodiment, the CD34⁺, CD45⁻ hematopoietic placental stemcells are fetal (non-maternal). In another embodiment, the CD34⁺, CD45⁻hematopoietic placental stem cells are maternal. In another embodiment,an isolated population of hematopoietic placental stem cells comprisesCD34⁺, CD45⁻ hematopoietic placental stem cells that are fetal(non-maternal). In another embodiment, an isolated population ofhematopoietic placental stem cells comprises CD34⁺, CD45⁺ hematopoieticplacental stem cells that are maternal.

In another aspect, provided herein are methods of isolating CD34⁺, CD45⁻hematopoietic placental stem cells. In one embodiment, the inventionprovides a method of isolating a CD34⁺, CD45⁻ placental stem cellpopulation, comprising selecting CD34⁺ cells from a population ofplacental cells to form an isolated population of CD34⁺ placental cells,and removing from said population of CD34⁺ placental cells CD45⁺ cells,wherein a CD34⁺, CD45⁻ placental stem cell population is produced. In aspecific embodiment, said selecting CD34⁺ cells is done byimmunoseparation. In another specific embodiment, said removing CD45⁺cells is done by immunoseparation. In another specific embodiment, saidselecting or said removing is done by flow cytometry.

In another aspect, provided herein is a method of supplementing a cellpopulation comprising adding a plurality of CD34⁺, CD45⁻ hematopoieticplacental stem cells to create a supplemented cell population, such thatthe supplemented cell population comprises substantially more CD34⁺,CD45⁻ cells than before said supplementing. In various specificembodiments in this context, “substantially more” means at least 1, 2,3, 4, 5, 6, 7, 8, 9 or at least 10% more. In other specific embodiments,the cell population to be supplemented comprises cord blood, placentalblood, peripheral blood, or a combination thereof. In more specificembodiments, the cell population to be supplemented is cord blood,placental blood, peripheral blood, or a combination thereof. In anothermore specific embodiment, the cell population to be supplementedcomprises nucleated cells isolated from cord blood, placental blood,peripheral blood, or a combination thereof. In other specificembodiments, the stem cell population to be supplemented comprises apopulation of hematopoietic stem cells, a population of adult stemcells, or a population of embryonic stem cells.

As used herein, the term “SH2” refers to an antibody that binds anepitope on the marker CD105. Thus, cells that are referred to as SH2⁺are CD105⁺.

As used herein, the terms “SH3” and SH4” refer to antibodies that bindepitopes present on the marker CD73. Thus, cells that are referred to asSH3⁺ and/or SH4⁺ are CD73⁺.

As used herein, the term “isolated stem cell” means a stem cell that issubstantially separated from other, non-stem cells of the tissue, e.g.,placenta, from which the stem cell is derived. A stem cell is “isolated”if at least 50%, 60%, 70%, 80%, 90%, 95%, or at least 99% of thenon-stem cells with which the stem cell is naturally associated, or stemcells displaying a different marker profile, are removed from the stemcell, e.g., during collection and/or culture of the stem cell.

As used herein, the term “population of isolated cells” means apopulation of cells that is substantially separated from other cells ofthe tissue, e.g., placenta, from which the population of cells isderived. A stem cell is “isolated” if at least 50%, 60%, 70%, 80%, 90%,95%, or at least 99% of the cells with which the population of cells, orcells from which the population of cells is derived, is naturallyassociated, i.e., stem cells displaying a different marker profile, areremoved from the stem cell, e.g., during collection and/or culture ofthe stem cell.

As used herein, the term “placental stem cell” refers to a stem cell orprogenitor cell, e.g., a multipotent cell, that is derived from amammalian placenta, regardless of morphology, cell surface markers, orthe number of passages after a primary culture. The term “placental stemcell” as used herein does not, however, refer to a trophoblast,cytotrophoblast, embryonic germ cell or embryonic stem cell. A cell isconsidered a “stem cell” if the cell retains at least one attribute of astem cell, e.g., a marker or gene expression profile associated with oneor more types of stem cells; the ability to replicate at least 10-40times in culture; multipotency, e.g., the ability to differentiate,either in vitro, in vivo or both, into cells of one or more of the threegerm layers; the lack of adult (i.e., differentiated) cellcharacteristics, or the like. The terms “placental stem cell” and“placenta-derived stem cell” may be used interchangeably. Unlessotherwise noted herein, the term “placental” includes the umbilicalcord. The adherent placental stem cells disclosed herein are, in certainembodiments, multipotent in vitro (that is, the cells differentiate invitro under differentiating conditions), multipotent in vivo (that is,the cells differentiate in vivo), or both.

As used herein, a stem cell is “positive” for a particular marker whenthat marker is detectable above background. For example, a placentalstem cell is positive for, e.g., CD73 because CD73 is detectable onplacental stem cells, e.g., by flow cytometry, in an amount detectablygreater than background (in comparison to, e.g., an isotype control). Acell is also positive for a marker when that marker can be used todistinguish the cell from at least one other cell type, or can be usedto select or isolate the cell when present or expressed by the cell. Inthe context of, e.g., antibody-mediated detection, “positive,” as anindication a particular cell surface marker is present, means that themarker is detectable using an antibody, e.g., a fluorescently-labeledantibody, specific for that marker; “positive” also means that a cellbears that marker in a amount that produces a signal, e.g., in acytometer, that is detectably above background. For example, a cell is“CD200⁺” where the cell is detectably labeled with an antibody specificto CD200, and the signal from the antibody is detectably higher than acontrol (e.g., background). Conversely, “negative” in the same contextmeans that the cell surface marker is not detectable using an antibodyspecific for that marker compared to background. For example, a cell is“CD34⁻” where the cell is not detectably labeled with an antibodyspecific to CD34. Unless otherwise noted herein, cluster ofdifferentiation (“CD”) markers are detected using antibodies. OCT-4 isdetermined to be present, and a cell is “OCT-4⁺” if OCT-4 is detectableusing RT-PCR.

As used herein, “isolating” placental stem cells, e.g., adherentplacental stem cells or CD34⁺, CD45⁻ stem cells, means to remove atleast 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95% or 99% of the cellswith which the stem cells are normally associated in the intactmammalian placenta. A stem cell from an organ is “isolated” when it ispresent in a population of cells that comprises fewer than 50% of thecells with which the stem cell is normally associated in the intactorgan. “Dim”, when associated with a cell marker, indicates that themarker is present detectably above background, but within about 5% toabout 10% above background.

As used herein, “hepatocyte” means a cell that appears visually,biochemically and/or by gene expression pattern to be a hepatocyte asthat term is normally understood. As used herein, “hepatogenic cell,”referring to a cell differentiated from a placental stem cell orumbilical cord stem cells, is a cell that displays one or morecharacteristics of a terminally-differentiated hepatocyte, whichcharacteristics are not found in a placental stem cell or umbilical cordstem cells, or are not found at the same level in a placental stem cellor umbilical cord stem cell (e.g., are detectably higher or lower in ahepatogenic cell when compared to a placental stem cell or umbilicalstem cell assayed for the characteristic under equivalent conditions),prior to differentiation into a hepatocyte or hepatogenic cell (e.g., aplacental stem cell or umbilical cord stem cell in an expansionculture). Thus, the various compositions, methods, and other embodimentsof the present application also encompass cells derived from placentalstem cells that have fully or partially differentiated into hepatocytes.

4. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Viability of placental stem cells from perfusion (A), amnion(B), chorion (C), or amnion-chorion plate (D), or umbilical cord stemcells (E). Numbers on X-axis designate placenta from which stem cellswere obtained.

FIG. 2: Percent HLA ABC⁻/CD45⁻/CD34⁻/CD133⁺ cells from perfusion (A),amnion (B), chorion (C), or amnion-chorion plate (D), or umbilical cordstem cells (E) as determined by FACSCalibur. Numbers on X-axis designateplacenta from which stem cells were obtained.

FIG. 3: Percent HLA ABC⁻/CD45⁻/CD34⁻/CD133⁺ cells from perfusion (A),amnion (B), chorion (C), or amnion-chorion plate (D), or umbilical cordstem cells (E), as determined by FACS Aria. Numbers on X-axis designateplacenta from which stem cells were obtained.

FIG. 4: HLA-G, CD10, CD13, CD33, CD38, CD44, CD90, CD105, CD117, CD200expression in stem cells derived from placental perfusate.

FIG. 5: HLA-G, CD10, CD13, CD33, CD38, CD44, CD90, CD105, CD117, CD200expression in stem cells derived from amnion.

FIG. 6: HLA-G, CD10, CD13, CD33, CD38, CD44, CD90, CD105, CD117, CD200expression in stem cells derived from chorion.

FIG. 7: HLA-G, CD10, CD13, CD33, CD38, CD44, CD90, CD105, CD117, CD200expression in stem cells derived from amnion-chorion plate.

FIG. 8: HLA-G, CD10, CD13, CD33, CD38, CD44, CD90, CD105, CD117, CD200expression in stem cells derived from umbilical cord.

FIG. 9: Average expression of HLA-G, CD10, CD13, CD33, CD38, CD44, CD90,CD105, CD117, CD200 expression in stem cells derived from perfusion (A),amnion (B), chorion (C), amnion-chorion plate (D) or umbilical cord (E).

FIG. 10: Average percentage of total cells from six matched humanplacental perfusate and umbilical cord units. X axis: percent cells, oftotal nucleated cells, of the phenotype shown on the Y-axis.

5. DETAILED DESCRIPTION 5.1 Production of Hepatocytes

In the sections and discussions that follow, it will be understood bythe skilled artisan that many of the various compositions and methodscan be performed on or using placental stem cells or umbilical cord stemcells that have differentiated, or have been differentiated, down thehepatocyte lineage.

In one aspect, provided herein are methods and compositions for theproduction of hepatocytes and/or hepatogenic cells from placenta-derivedcells, particularly placental stem cells or umbilical cord stem cells.As used herein, “placental stem cells” or “umbilical cord stem cells”means adherent stem cells unless otherwise specified. Stem cells may beobtained from a mammalian placenta or umbilical cord by perfusion (see,e.g., Hariri, U.S. Pat. Nos. 7,045,148 and 7,255,879, which are herebyincorporated herein in their entireties. Stem cells may also be obtainedfrom placenta or umbilical cord by disruption (e.g., maceration) of aplacenta or part thereof (see, e.g., Section 6.2, below). Cellsdisplaying hepatocyte characteristics, e.g., hepatocytes and/orhepatogenic cells, may be obtained from placental stem cells. Thesecells are useful in the treatment of diseases, disorders or conditionsassociated with, for example, cirrhosis of the liver, including, but notlimited to cirrhosis caused by alcohol ingestion, ingestion of hepatictoxins such as those found in, e.g., mushrooms of the genus Amanita, orcaused by viral infections, e.g., hepatitis A, B, C, D, or E infection.

In one embodiment, differentiable cells, such as stem cells, may beobtained from the placenta or umbilical cord as follows. Primarycultures of mononuclear cells (MNCs) are isolated from placentas, e.g.,from human placenta perfusates or from physically and/orenzymatically-disrupted placental tissue. The placentas are obtainedfollowing birth of full-term infants under informed consent of thedonors. Briefly, for perfusion, umbilical vessels are cannulated thenconnected to a flow-controlled circuit, and the placenta is perfused at,e.g., 1 mL/min (room temperature, up to 24 hours) with Dulbecco'smodified Eagle's medium (DMEM, Gibco/BRL) containing high glucose, 1%heparin and penicillin/streptomycin. Placenta perfusate (750 mL) is thenpooled, centrifuged, and the cell pellet resuspended in PBS containing1% fetal calf serum (FBS) then separated by differential gradientdensity centrifugation through LYMPHOPREP™ (Gibco/BRL). The buffy-coatinterface containing mononucleated cells including adherent placentalstem cells are recovered, resuspended in DMEM/10% FBS, plated onfibronectin-coated (Sigma) Falcon plates and incubated at 37° C. with 5%humidified CO₂. After a 24-hour incubation the nonadherent cells arediscarded and the adherent cells are maintained and expanded in freshculture media; individual cell colonies develop between 10 and 18 daysand are expanded as placental stem cell lines.

Human adherent placental stem cells display fibroblast-like morphologyin culture and are HLA-class I positive. Using FACS analysis these cellsdo not express the hematopoietic markers CD34 or CD45. However, they doexpress the multipotential cellular markers CD10 (CALLA), CD29 (β₁integrin), CD54 (ICAM-1), CD90 (Thy-1) as well as SH2 (CD105), SH3(CD73) and CD200. Under standard growth conditions the doubling time forplacental stem cells is about 18 to 36 hours, and the cells maintainthis phenotype for greater than 40 population doublings in vitro. Humanadherent placental stem cells are distinguishable from human embryonicstem cells or embryonic germ cells in that human embryonic stem cells orgerm cells are obtained only from the inner cell mass of the blastula orfetal gonads, not placentas. Human adherent placental stem cells arealso distinguishable from mesenchymal stem cells from, e.g., bonemarrow, cord blood or peripheral blood, or bone marrow-derived stemcells, in that placental stem cells form embryoid-like bodies inculture, while mesenchymal stem cells or bone marrow-derived stem cellsdo not, and placental stem cells display unique gene expression patternrelative to mesenchymal stem cells. See U.S. patent application Ser. No.11/648,813, filed Dec. 28, 2006, the disclosure of which is herebyincorporated herein by reference in its entirety.

Placental stem cells may be differentiated to hepatocytes by culturingin culture medium comprising sodium butyrate or by encapsulating thecells in a suitable microcapsule polymer, e.g. alginate-poly-L-lysine.Hepatocytes can be produced from placenta-derived stem cells asdescribed above, and maintained or cultured as described in below.Hepatocyte differentiation can be assessed using flow cytometry andmonitoring for particular gene expression or enzymatic activity asdescribed below.

5.2 Placental Stem Cells and Placental Stem Cell Populations

In one aspect, the methods provided herein use adherent placental stemcells, that is, stem cells obtainable from a placenta or part thereof,e.g., amnion, chorion, amnion/chorion plate, umbilical cord, etc., that(1) adhere to a tissue culture substrate; and (2) differentiate into oneor more non-placental cell types, and/or cells having tissue-specificcell characteristics, under the appropriate differentiation conditions.Placental stem cells are not derived from, nor are they derivable from,blood, e.g., placental blood or umbilical cord blood, or from bonemarrow.

Placental stem cells can be either fetal or maternal in origin (that is,can have the genotype of either the mother or fetus). Populations ofplacental stem cells, or populations of cells comprising placental stemcells, can comprise placental stem cells that are solely fetal ormaternal in origin, or can comprise a mixed population of placental stemcells of both fetal and maternal origin. The placental stem cells, andpopulations of cells comprising the placental stem cells, can beidentified and selected by the morphological, marker, and culturecharacteristics discussed below.

5.2.1 Physical and Morphological Characteristics

The placental stem cells used in the methods disclosed herein, whencultured in primary culture or in cell culture, adhere to the tissueculture substrate, e.g., tissue culture container surface (e.g., tissueculture plastic). Placental stem cells in culture, e.g., on a tissueculture surface, assume a generally fibroblastoid appearance, with anumber of cyotplasmic processes extending from the central cell body.The placental stem cells are, however, morphologically distinguishablefrom fibroblasts cultured under the same conditions, as the placentalstem cells exhibit a greater number of such processes than dofibroblasts. Morphologically, placental stem cells are alsodistinguishable from hematopoietic stem cells, which generally assume amore rounded, or cobblestone, morphology in culture.

5.2.2 Cell Surface, Molecular and Genetic Markers

Adherent placental stem cells, and populations of adherent placentalstem cells, useful in the methods and compositions described herein,express a plurality of markers that can be used to identify and/orisolate the stem cells, or populations of cells that comprise the stemcells. The placental stem cells, and stem cell populations (that is, twoor more placental stem cells) described herein include stem cells andstem cell-containing cell populations obtained directly from theplacenta, or any part thereof (e.g., amnion, chorion, placentalcotyledons, umbilical cord, and the like). Placental stem cellpopulations also includes populations of (that is, two or more)placental stem cells in culture, and a population in a container, e.g.,a bag. Placental stem cells are not, however, trophoblasts.

The placental stem cells described herein are multipotent in that theycan be differentiated in vitro into cells representative of the threegerm layers, e.g., adipocytic cells, chondrocytic cells, hepatic cells,neurogenic cells, cardiac cells, and the like. The placental stem cellsdescribed herein, however, need not differentiate in vivo to beconsidered multipotent, or to be useful. The term “placental stem cell,”therefore, encompasses cells described herein that differentiate invitro but not in vivo, differentiate in vivo but not in vitro, or bothin vitro and in vivo. In one embodiment, the placental stem cellsprovided herein can be differentiated in vitro into cells representativeof one or more of the three germ layers, but do not differentiate invivo, e.g., in a NOD-SCID mouse.

Adherent (non-hematopoietic) placental stem cells generally express themarkers CD73, CD105, CD200, HLA-G, and/or OCT-4, and do not expressCD34, CD38, or CD45. Placental stem cells can also express HLA-ABC(MHC-1), but generally do not express HLA-DR. In a specific embodiment,adherent placental stem cells are CD10⁺, CD34⁻, CD105⁺ and CD200⁺. Thesemarkers can be used to identify placental stem cells, and to distinguishplacental stem cells from other stem cell types. Because the placentalstem cells can express CD73 and CD105, they can have mesenchymal stemcell-like characteristics. However, because the placental stem cells canexpress CD200 and HLA-G, a fetal-specific marker, they can bedistinguished from mesenchymal stem cells, e.g., bone marrow-derivedmesenchymal stem cells, which express neither CD200 nor HLA-G. In thesame manner, the lack of expression of CD34, CD38 and/or CD45 identifiesthe placental stem cells as non-hematopoietic stem cells. Such placentalstem cells, and populations of cells comprising such placental stemcells, can be differentiated into hepatocytes, hepatogenic cells,populations of hepatocytes, populations of hepatogenic cells, andcombinations of the foregoing.

In one embodiment, the methods and compositions provided herein use anisolated placental stem cell that is CD200⁺ and HLA-G⁺. In specificembodiments, said stem cell is also CD73⁺ and CD105⁺. In anotherspecific embodiment, said stem cell is also CD34, CD38⁻ or CD45⁻. In amore specific embodiment, said stem cell is also CD34⁻, CD38⁻, CD45⁻,CD73⁺ and CD105⁺. In another specific embodiment, said stem cell hasbeen expanded, for example, passaged at least once, at least threetimes, at least five times, at least 10 times, at least 15 times, or atleast 20 times.

In another embodiment, the methods and compositions provided herein usean isolated cell population comprising a plurality of placental stemcells that are CD200⁺, HLA-G⁺. In various embodiments, at least 10%, atleast 20%, at least 30%, at least 40%, at least 50% at least 60%, atleast 70%, at least 80%, at least 90%, or at least 95% of said placentalstem cells in said population are said CD200⁺, HLA-G⁺ stem cells. In aspecific embodiment of the isolated populations, said stem cells arealso CD73⁺ and CD105′. In another specific embodiment, said stem cellsare also CD34⁻, CD38⁻ or CD45⁻. In a more specific embodiment, said stemcells are also CD34⁻, CD38⁻, CD45⁻, CD73⁺ and CD105⁺. In anotherembodiment, said isolated population produces one or more embryoid-likebodies when cultured under conditions that allow the formation ofembryoid-like bodies. In another specific embodiment, said populationhas been expanded, for example, passaged at least once, at least threetimes, at least five times, at least 10 times, at least 15 times, or atleast 20 times.

In another embodiment, the methods and compositions provided herein usean isolated placental stem cell that is CD73⁺, CD105⁺, CD200⁺. In aspecific embodiment of said populations, said stem cell is also HLA-G⁺.In another specific embodiment, said stem cell is also CD34⁻, CD38⁻ orCD45⁻. In another specific embodiment, said stem cell is also CD34⁻,CD38⁻ and CD45⁻. In a more specific embodiment, said stem cell is alsoCD34⁻, CD38⁻, CD45⁻, and HLA-G⁺. In another specific embodiment, saidstem cell has been expanded, for example, passaged at least once, atleast three times, at least five times, at least 10 times, at least 15times, or at least 20 times.

In another embodiment, the methods and compositions provided herein usean isolated cell population comprising a plurality of placental stemcells that are CD73⁺, CD105⁺, CD200⁺. In various embodiments, at least10%, at least 20%, at least 30%, at least 40%, at least 50% at least60%, at least 70%, at least 80%, at least 90%, or at least 95% of saidplacental stem cells in said population are said CD73⁺, CD105⁺, CD200⁺cells. In a specific embodiment of said populations, said stem cells areHLA-G⁺. In another specific embodiment, said stem cells are CD34⁻, CD38⁻or CD45⁻. In another specific embodiment, said stem cells are CD34⁻,CD38⁻ and CD45⁻. In a more specific embodiment, said stem cells areCD34⁻, CD38⁻, CD45⁻, and HLA-G⁺. In another specific embodiment, saidpopulation of cells produces one or more embryoid-like bodies whencultured under conditions that allow the formation of embryoid-likebodies. In another specific embodiment, said population has beenexpanded, for example, passaged at least once, at least three times, atleast five times, at least 10 times, at least 15 times, or at least 20times.

In another embodiment, the methods and compositions provided herein usean isolated placental stem cell that is CD200⁺, OCT-4⁺. In a specificembodiment, said stem cell is also CD73⁺ and CD105⁺. In another specificembodiment, said stem cell is also IILA-G⁺. In another specificembodiment, said stem cell is also CD34⁻, CD38⁻ and CD45⁻. In a morespecific embodiment, said stem cell is also CD34⁻, CD38⁻, CD45⁻, CD73⁺,CD105⁺ and HLA-G⁺. In another specific embodiment, said stem cell hasbeen expanded, for example, passaged at least once, at least threetimes, at least five times, at least 10 times, at least 15 times, or atleast 20 times.

In another embodiment, the methods and compositions provided herein usean isolated cell population comprising a plurality of placental stemcells that are CD200′, OCT-4⁺. In various embodiments, at least 10%, atleast 20%, at least 30%, at least 40%, at least 50% at least 60%, atleast 70%, at least 80%, at least 90%, or at least 95% of said placentalstem cells in said population are said CD200⁺, OCT-4⁺ cells. In aspecific embodiment, said stem cells are CD73⁺ and CD105⁺. In anotherspecific embodiment, said stem cells are HLA-G⁺. In another specificembodiment, said stem cells are CD34⁻, CD38⁻ and CD45⁻. In a morespecific embodiment, said stem cells are CD34⁻, CD38⁻, CD45⁻, CD73⁺,CD105⁺ and HLA-G⁺. In another specific embodiment, the populationproduces one or more embryoid-like bodies when cultured under conditionsthat allow the formation of embryoid-like bodies. In another specificembodiment, said population has been expanded, for example, passaged atleast once, at least three times, at least five times, at least 10times, at least 15 times, or at least 20 times.

In another embodiment, the methods and compositions provided herein usean isolated placental stem cell that is CD73⁺, CD105⁺ and HLA-G⁺. In aspecific embodiment of the above plurality, said stem cell is alsoCD34⁻, CD38⁻ or CD45⁻. In another specific embodiment, said stem cell isalso CD34⁻, CD38⁻ and CD45⁻. In another specific embodiment, said stemcells are also OCT-4⁺. In another specific embodiment, said stem cell isalso CD200⁺. In a more specific embodiment, said stem cell is alsoCD34⁻, CD38⁻, CD45⁻, OCT-4⁺ and CD200⁺. In another specific embodiment,said stem cell has been expanded, for example, passaged at least once,at least three times, at least five times, at least 10 times, at least15 times, or at least 20 times.

In another embodiment, the methods and compositions provided herein usean isolated cell population comprising a plurality of placental stemcells that are CD73⁺, CD105⁺ and HLA-G⁺. In various embodiments, atleast 10%, at least 20%, at least 30%, at least 40%, at least 50% atleast 60%, at least 70%, at least 80%, at least 90%, or at least 95% ofsaid placental stem cells in said population are said CD73⁺, CD105⁺ andHLA-G⁺ cells. In a specific embodiment of the above plurality, said stemcells are also CD34⁻, CD38⁻ or CD45⁻. In another specific embodiment,said stem cells are also CD34⁻, CD38⁻ and CD45⁻. In another specificembodiment, said stem cells are also OCT-4⁺. In another specificembodiment, said stem cells are also CD200⁺. In a more specificembodiment, said stem cells are also CD34, CD38⁻, CD45⁻, OCT-4⁺ andCD200⁺. In another specific embodiment, said population has beenexpanded, for example, passaged at least once, at least three times, atleast five times, at least 10 times, at least 15 times, or at least 20times.

In another embodiment, the methods and compositions provided herein usean isolated cell population comprising a plurality of placental stemcells that are CD73⁺, CD105⁺ stem cells, wherein said plurality formsone or more embryoid-like bodies under conditions that allow formationof embryoid-like bodies. In various embodiments, at least 10%, at least20%, at least 30%, at least 40%, at least 50% at least 60%, at least70%, at least 80%, at least 90%, or at least 95% of said placental stemcells in said population are said CD73⁺, CD105⁺ stem cells. In aspecific embodiment, said stem cells are also CD34⁻, CD38⁻ or CD45⁻. Inanother specific embodiment, said stem cells are also CD34⁻, CD38⁻ andCD45⁻. In another specific embodiment, said stem cells are also OCT-4⁺.In a more specific embodiment, said stem cells are also OCT-4⁺, CD34⁻,CD38⁻ and CD45⁻. In another specific embodiment, said population hasbeen expanded, for example, passaged at least once, at least threetimes, at least five times, at least 10 times, at least 15 times, or atleast 20 times.

In another embodiment, the methods and compositions provided herein usean isolated cell population comprising a plurality of placental stemcells that are OCT-4⁺ stem cells, wherein said population forms one ormore embryoid-like bodies when cultured under conditions that allow theformation of embryoid-like bodies. In various embodiments, at least 10%,at least 20%, at least 30%, at least 40%, at least 50% at least 60%, atleast 70%, at least 80%, at least 90%, or at least 95% of said placentalcells in said population are said OCT4⁺ stem cells. In a specificembodiment of the above populations, said stem cells are CD73⁺ andCD105⁺. In another specific embodiment, said stem cells are CD34⁻,CD38⁻, or CD45⁻. In another specific embodiment, said stem cells areCD200⁺. In a more specific embodiment, said stem cells are CD73⁺,CD105⁺, CD200⁺, CD34⁻, CD38⁻, and CD45⁻. In another specific embodiment,said population has been expanded, for example, passaged at least once,at least three times, at least five times, at least 10 times, at least15 times, or at least 20 times.

In another embodiment, the methods and compositions provided herein usean isolated placental stem cell that is, or a cell population comprisinga plurality of placental stem cells that are, CD29⁺, CD44⁺, CD73⁺,CD90⁺, CD105⁺, CD200⁺, CD34⁻ and CD133⁻.

In another embodiment, the methods and compositions provided herein usean isolated placental stem cell that is CD10⁺, CD34⁺, CD105⁺, andCD200′. Further provided herein is an isolated population of cells,e.g., placental stem cells, wherein at least about 70%, at least about80%, at least about 90%, at least about 95% or at least about 99% ofsaid placental stem cells are CD10⁺, CD34⁻, CD105⁺, CD200⁺. In aspecific embodiment of the above embodiments, said stem cells areadditionally CD90⁺ and CD45⁻. In a specific embodiment, said stem cellor population of placental stem cells is isolated away from placentalcells that are not stem cells. In another specific embodiment, said stemcell or population of placental stem cells is isolated away fromplacental stem cells that do not display these characteristics. Inanother specific embodiment, said isolated placental stem cell isnon-maternal in origin. In another specific embodiment, at least about90%, at least about 95%, or at least about 99% of said cells in saidisolated population of placental stem cells, are non-maternal in origin.

In another embodiment, the methods and compositions provided herein usean isolated placental stem cell that is HLA-A,B,C⁻, CD45⁻, CD133⁻ andCD34⁻. Further provided herein is the use of an isolated population ofplacental stem cells, wherein at least about 70%, at least about 80%, atleast about 90%, at least about 95% or at least about 99% of saidplacental stem cells are HLA-A,B,C⁻, CD45⁻, CD133 and CD34⁻. In aspecific embodiment, said stem cell or population of placental stemcells is isolated away from placental cells that are not stem cells. Inanother specific embodiment, said population of placental stem cells isisolated away from placental stem cells that do not display thesecharacteristics. In another specific embodiment, said isolated placentalstem cell is non-maternal in origin. In another specific embodiment, atleast about 90%, at least about 95%, or at least about 99% of said cellsin said isolated population of placental stem cells, are non-maternal inorigin. In another embodiment, the HLA-A,B,C⁻, CD45⁻, CD133 and CD34⁻placental stem cell is a stem cell isolated from placental perfusate. Inanother embodiment, the HLA-A,B,C⁻, CD45⁻, CD133⁻ and CD34⁻ placentalstem cell is a stem cell isolated by physical and/or enzymaticdisruption of placental tissue.

In another embodiment, the methods and compositions provided herein anisolated placental stem cell that is CD10⁺, CD13⁺, CD33⁺, CD45⁻, CD1 ITand CD133⁻. Further provided herein is an isolated population ofplacental stem cells, wherein at least about 70%, at least about 80%, atleast about 90%, at least about 95% or at least about 99% of saidplacental stem cells are CD10⁺, CD1³, CD33⁺, CD45⁻, CD117⁻ and CD133⁻.In a specific embodiment, said stem cell or population of placental stemcells is isolated away from placental cells that are not stem cells. Inanother specific embodiment, said isolated placental stem cell isnon-maternal in origin. In another specific embodiment, at least about90%, at least about 95%, or at least about 99% of said cells in saidisolated population of placental stem cells, are non-maternal in origin.In another specific embodiment, said stem cell or population ofplacental stem cells is isolated away from placental stem cells that donot display these characteristics. In another embodiment, providedherein is a method of obtaining a placental stem cell that is CD10⁺,CD13⁺, CD33⁺, CD45⁻, CD117 and CD133⁻ comprising isolating said cellfrom placental perfusate. In another embodiment, the HLA-A,B,C⁻, CD45⁻,CD133⁻ and CD34⁻ placental stem cell is a stem cell isolated by physicaland/or enzymatic disruption of placental tissue.

In another embodiment, the methods and compositions provided herein anisolated placental stem cell that is CD10⁻, CD33⁻, CD44⁺, CD45⁻, andCD117⁻ T. Further provided herein is an isolated population of placentalstem cells, wherein at least about 70%, at least about 80%, at leastabout 90%, at least about 95% or at least about 99% of said placentalstem cells are CD10⁻, CD33⁻, CD44⁺, CD45⁻, and CD117⁻. In a specificembodiment, said stem cell or population of placental stem cells isisolated away from placental cells that are not stem cells. In anotherspecific embodiment, said isolated placental stem cell is non-maternalin origin. In another specific embodiment, at least about 90%, at leastabout 95%, or at least 99% of said cells in said isolated population ofplacental stem cells, are non-maternal in origin. In another specificembodiment, said stem cell or population of placental stem cells isisolated away from placental stem cells that do not display thesecharacteristics. In another embodiment, provided herein is a method ofobtaining a placental stem cell that is CD10⁻, CD33⁻, CD44⁺, CD45⁻,CD117⁻ comprising isolating said cell from placental perfusate. Inanother embodiment, the HLA-A,B,C⁻, CD45⁻, CD133⁻ and CD34⁻ placentalstem cell is a stem cell isolated by physical and/or enzymaticdisruption of placental tissue.

In another embodiment, the methods and compositions provided herein usean isolated placental stem cell that is CD10⁻, CD13⁻, CD33⁻, CD45⁻, andCD117⁻. Further provided herein an isolated population of placental stemcells, wherein at least about 70%, at least about 80%, at least about90%, at least about 95% or at least about 99% of said placental stemcells are CD10⁻, CD13⁻, CD33⁻, CD45⁻, and CD117⁻. In a specificembodiment, said stem cell or population of placental stem cells isisolated away from placental cells that are not stem cells. In anotherspecific embodiment, said isolated placental stem cell is non-maternalin origin. In another specific embodiment, at least about 90%, at leastabout 95%, or at least 99% of said cells in said isolated population ofplacental stem cells, are non-maternal in origin. In another specificembodiment, said stem cell or population of placental stem cells isisolated away from placental stem cells that do not display thesecharacteristics. In another embodiment, provided herein is a method ofobtaining a placental stem cell that is CD10⁻, CD13⁻, CD33⁻, CD45⁻, andCD117⁻ comprising isolating said cell from placental perfusate. Inanother embodiment, the HLA-A,B,C⁻, CD45⁻, CD133⁻ and CD34⁻ placentalstem cell is a stem cell isolated by physical and/or enzymaticdisruption of placental tissue.

In another embodiment, the methods and compositions provided herein usean isolated placental stem cell that is HLA A,B,C⁻, CD45⁻, CD34⁻,CD133⁻, positive for CD10, CD13, CD38, CD44, CD90, CD105, CD200 and/orHLA-G, and/or negative for CD117. In another embodiment, the isolatedpopulation of placental stem cells used in the methods and compositionsprovided herein are HLA A,B,C⁻, CD45⁻, CD34⁻, CD133⁻, and at least about20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%,90%, 95%, 98% or about 99% of the stem cells in the population arepositive for CD10, CD13, CD38, CD44, CD90, CD105, CD200 and/or HLA-G,and/or negative for CD117. In a specific embodiment, said stem cell orpopulation of placental stem cells is isolated away from placental cellsthat are not stem cells. In another specific embodiment, said isolatedplacental stem cell is non-maternal in origin. In another specificembodiment, at least about 90%, at least about 95%, or at least about99%, of said cells in said isolated population of placental stem cells,are non-maternal in origin. In another specific embodiment, said stemcell or population of placental stem cells is isolated away fromplacental stem cells that do not display these characteristics. Inanother embodiment, provided herein is a method of obtaining a placentalstem cell that is HLA A,B,C⁻, CD45⁻, CD34⁻, CD133⁻ and positive forCD10, CD13, CD38, CD44, CD90, CD105, CD200 and/or HLA-G, and/or negativefor CD117, comprising isolating said cell from placental perfusate.

In another embodiment, the methods and compositions provided herein usea placental stem cell that is CD200⁺ and CD10⁺, as determined byantibody binding, and CD117⁺, as determined by both antibody binding andRT-PCR, or a population of such cells, or a population of cellscomprising such isolated placental stem cells. In another embodiment,the methods and compositions provided herein use a placental stem cellthat is CD10⁺, CD29⁻, CD54⁺, CD200⁺, HLA-G⁺, HLA class F andβ-2-microglobulin. In another embodiment, provided herein are placentalstem cells, wherein the expression of at least one marker is at leasttwo-fold higher than for a mesenchymal stem cell (e.g., a bonemarrow-derived mesenchymal stem cell). In another specific embodiment,said isolated placental stem cell is non-maternal in origin. In anotherspecific embodiment, at least about 90%, at least about 95%, or at least99%, of said cells in said isolated population of placental stem cells,are non-maternal in origin.

In another embodiment, placental stem cells used in the methods andcompositions provided herein are positive for cytokeratin 18. In anotherembodiment, provided herein is a population of placental stem cells, orcells differentiated therefrom, at least 50%, 70%, 80%, 90%, 95% or 99%of which are positive for cytokeratin 18. In another embodiment,provided herein is a population of cells comprising placental stemcells, or cells differentiated therefrom, wherein at least 50%, 70%,80%, 90%, 95% or 99% of the placental stem cells or cells differentiatedtherefrom are positive for cytokeratin 18. In another embodiment, theinvention provides a method of isolating a placental stem cell, orpopulation of placental stem cells, or cells differentiated therefrom,comprising selecting a cytokeratin 18+ placental stem cell, orcytokeratin 18+ placental stem cells, and isolating said stem cell orstem cells from other placental cells.

In another embodiment, the methods and compositions provided herein usean isolated population of placental stem cells, wherein a plurality ofsaid placental stem cells are positive for aldehyde dehydrogenase(ALDH), as assessed by an aldehyde dehydrogenase activity assay. Suchassays are known in the art (see, e.g., Bostian and Betts, Biochem. J.,173, 787, (1978)). In a specific embodiment, said ALDH assay usesALDEFLUOR® (Aldagen, Inc., Ashland, Oreg.) as a marker of aldehydedehydrogenase activity. In another specific embodiment, said pluralityis between about 3% and about 25% of cells in said population of cells.In another embodiment, the methods and compositions provided herein usea population of placental stem cells, wherein a plurality of saidplacental stem cells are positive for aldehyde dehydrogenase, asassessed by an aldehyde dehydrogenase activity assay that usesALDEFLUOR® as an indicator of aldehyde dehydrogenase activity. In aspecific embodiment, said plurality is between about 3% and about 25% ofcells in said population of cells. In another embodiment, saidpopulation of placental stem cells or umbilical cord stem cells shows atleast three-fold, or at least five-fold, higher ALDH activity than apopulation of bone marrow-derived mesenchymal stem cells having the samenumber of cells and cultured under the same conditions.

In a specific embodiment of the above-mentioned placental stem cells,the placental stem cells constitutively secrete IL-6, IL-8 and monocytechemoattractant protein (MCP-1).

Each of the above-referenced placental stem cells, or pluralities ofplacental stem cells, can comprise placental stem cells obtained andisolated directly from a mammalian placenta, or placental stem cellsthat have been cultured and passaged at least 1, 2, 3, 4, 5, 6, 7, 8, 9,10, 12, 14, 16, 18, 20, 25, 30, 35, 40 or more times, or a combinationthereof:

The pluralities of placental stem cells described above can compriseabout, at least, or no more than, 1×10⁵, 5×10⁵, 1×10⁶, 5×10⁶, 1×10⁷,5×10⁷, 1×10⁸, 5×10⁸, 1×10⁹, 5×10⁹, 1×10¹⁰, 5×10¹⁰, 1×10¹¹ or moreplacental stem cells.

5.2.3 Selecting and Producing Placental Stem Cell Populations

In another embodiment, provided herein is a method of selecting aplurality of placental stem cells from a plurality of placental cells,from which hepatocytes and/or hepatogenic cells can be differentiated,comprising selecting a population of placental cells wherein at least10%, at least 20%, at least 30%, at least 40%, at least 50% at least60%, at least 70%, at least 80%, at least 90%, or at least 95% of saidcells are CD200⁺, HLA-G⁺ placental stem cells. In a specific embodiment,said selecting comprises selecting stem cells that are also CD73⁺ andCD105⁺. In another specific embodiment, said selecting comprisesselecting stem cells that are also CD34, CD38⁻ or CD45⁻. In anotherspecific embodiment, said selecting comprises selecting placental stemcells that are also CD34⁻, CD38⁻, CD45⁻, CD73⁺ and CD105⁺. In anotherspecific embodiment, said selecting also comprises selecting a pluralityof placental stem cells that forms one or more embryoid-like bodies whencultured under conditions that allow the formation of embryoid-likebodies.

In another embodiment, provided herein is a method of selecting aplurality of placental stem cells from a plurality of placental cells,comprising selecting a plurality of placental cells wherein at least10%, at least 20%, at least 30%, at least 40%, at least 50% at least60%, at least 70%, at least 80%, at least 90%, or at least 95% of saidcells are CD73⁺, CD105⁺, CD200⁺ placental stem cells. In a specificembodiment, said selecting comprises selecting stem cells that are alsoHLA-G⁺. In another specific embodiment, said selecting comprisesselecting placental stem cells that are also CD34⁻, CD38⁻ or CD45⁻. Inanother specific embodiment, said selecting comprises selectingplacental stem cells that are also CD34⁻, CD38⁻ and CD45⁻. In anotherspecific embodiment, said selecting comprises selecting placental stemcells that are also CD34⁻, CD38⁻, CD45⁻, and HLA-G⁺. In another specificembodiment, said selecting additionally comprises selecting a populationof placental cells that produces one or more embryoid-like bodies whenthe population is cultured under conditions that allow the formation ofembryoid-like bodies.

In another embodiment, provided herein is a method of selecting aplurality of placental stem cells from a plurality of placental cells,comprising selecting a plurality of placental cells wherein at least10%, at least 20%, at least 30%, at least 40%, at least 50% at least60%, at least 70%, at least 80%, at least 90%, or at least 95% of saidcells are CD200⁺, OCT-4⁺ placental stem cells. In a specific embodiment,said selecting comprises selecting placental stem cells that are alsoCD73⁺ and CD105⁺. In another specific embodiment, said selectingcomprises selecting placental stem cells that are also HLA-G⁺. Inanother specific embodiment, said selecting comprises selectingplacental stem cells that are also CD34⁻, CD38⁻ and CD45⁻. In anotherspecific embodiment, said selecting comprises selecting placental stemcells that are also CD34⁻, CD38⁻, CD45⁻, CD73⁺, CD105⁺ and HLA-G⁺.

In another embodiment, provided herein is a method of selecting aplurality of placental stem cells from a plurality of placental cells,comprising selecting a plurality of placental cells wherein at least10%, at least 20%, at least 30%, at least 40%, at least 50% at least60%, at least 70%, at least 80%, at least 90%, or at least 95% of saidcells are CD73⁺, CD105⁺ and HLA-G⁺ placental stem cells. In a specificembodiment, said selecting comprises selecting placental stem cells thatare also CD34⁻, CD38⁻ or CD45⁻. In another specific embodiment, saidselecting comprises selecting placental stem cells that are also CD34⁻,CD38⁻ and CD45⁻. In another specific embodiment, said selectingcomprises selecting placental stem cells that are also CD200⁺. Inanother specific embodiment, said selecting comprises selectingplacental stem cells that are also CD34⁻, CD38⁻, CD45⁻, OCT-4⁺ andCD200⁺.

In another embodiment, provided herein is a method of selecting aplurality of placental stem cells from a plurality of placental cells,comprising selecting a plurality of placental cells wherein at least10%, at least 20%, at least 30%, at least 40%, at least 50% at least60%, at least 70%, at least 80%, at least 90%, or at least 95% of saidcells are CD73⁺, CD105⁺ placental stem cells, and wherein said pluralityforms one or more embryoid-like bodies under conditions that allowformation of embryoid-like bodies. In a specific embodiment, saidselecting comprises selecting placental stem cells that are also CD34⁻,CD38⁻ or CD45⁻. In another specific embodiment, said selecting comprisesselecting placental stein cells that are also CD34⁻, CD38⁻ and CD45⁻. Inanother specific embodiment, said selecting comprises selectingplacental stem cells that are also OCT-4⁺. In a more specificembodiment, said selecting comprises selecting placental stem cells thatare also OCT-4⁺, CD34⁻, CD38⁻ and CD45⁻.

In another embodiment, provided herein is a method of selecting aplurality of placental stem cells from a plurality of placental cells,comprising selecting a plurality of placental cells wherein at least10%, at least 20%, at least 30%, at least 40%, at least 50% at least60%, at least 70%, at least 80%, at least 90%, or at least 95% of saidisolated placental cells are OCT4⁺ stem cells, and wherein saidplurality forms one or more embryoid-like bodies under conditions thatallow formation of embryoid-like bodies. In a specific embodiment, saidselecting comprises selecting placental stem cells that are also CD73⁺and CD105⁺. In another specific embodiment, said selecting comprisesselecting placental stem cells that are also CD34⁻, CD38⁻, or CD45⁻. Inanother specific embodiment, said selecting comprises selectingplacental stem cells that are also CD200⁺. In a more specificembodiment, said selecting comprises selecting placental stem cells thatare also CD73⁺, CD105⁺, CD200⁺, CD34, CD38⁻, and CD45⁻.

Also provided herein are methods of producing populations, orpluralities, of placental stem cells; such cells can be used in themethods and compositions provided herein. For example, provided hereinis a method of producing a cell population, comprising selecting any ofthe pluralities of placental stem cells described above, and isolatingthe plurality of placental stem cells from other cells, e.g., otherplacental cells. In a specific embodiment, provided herein is a methodof producing a cell population comprising selecting placental cells,wherein said placental cells (a) adhere to a substrate, and (b) expressCD200 and HLA-G, or express CD73, CD105, and CD200, or express CD200 andOCT-4, or express CD73, CD105, and HLA-G, or express CD73 and CD105 andfacilitate the formation of one or more embryoid-like bodies in apopulation of placental cells that comprise the stem cell, when saidpopulation is cultured under conditions that allow formation ofembryoid-like bodies, or express OCT-4 and facilitate the formation ofone or more embryoid-like bodies in a population of placental cells thatcomprise the stem cell, when said population is cultured underconditions that allow formation of embryoid-like bodies.

In a more specific embodiment, provided herein is a method of producinga cell population comprising selecting placental stem cells that (a)adhere to a substrate, and (b) express CD200 and HLA-G; and isolatingsaid placental stem cells from other cells to form a cell population. Inanother specific embodiment, provided herein is a method of producing acell population comprising selecting placental stem cells that (a)adhere to a substrate, and (b) express CD73, CD105, and CD200; andisolating said placental stem cells from other cells to form a cellpopulation. In another specific embodiment, provided herein is a methodof producing a cell population comprising selecting placental stem cellsthat (a) adhere to a substrate, and (b) express CD200 and OCT-4; andisolating said placental stem cells from other cells to form a cellpopulation. In another specific embodiment, provided herein is a methodof producing a cell population comprising selecting placental stem cellsthat (a) adhere to a substrate, (b) express CD73 and CD105, and (c) formembryoid-like bodies when cultured under conditions allowing theformation of embryoid-like bodies; and isolating said placental stemcells from other cells to form a cell population. In another specificembodiment, provided herein is a method of producing a cell populationcomprising selecting placental stem cells that (a) adhere to asubstrate, and (b) express CD73, CD105, and HLA-G; and isolating saidplacental stem cells from other cells to form a cell population. Amethod of producing a cell population comprising selecting placentalstem cells that (a) adhere to a substrate, (b) express OCT-4, and (c)form embryoid-like bodies when cultured under conditions allowing theformation of embryoid-like bodies; and isolating said placental stemcells from other cells to form a cell population.

5.2.4 Growth in Culture

The growth of the placental stem cells described herein, as for anymammalian cell, depends in part upon the particular medium selected forgrowth. Under optimum conditions, placental stem cells typically doublein number in 3-5 days. During culture, the placental stem cells providedherein adhere to a substrate in culture, e.g. the surface of a tissueculture container (e.g., tissue culture dish plastic, fibronectin-coatedplastic, and the like) and form a monolayer.

Populations of isolated placental cells that comprise the placental stemcells provided herein, when cultured under appropriate conditions, formembryoid-like bodies, that is, three-dimensional clusters of cells growatop the adherent stem cell layer. Cells within the embryoid-like bodiesare expected to express markers associated with very early stem cells,e.g., OCT-4, Nanog, SSEA3 and SSEA4. Cells within the embryoid-likebodies are typically not adherent to the culture substrate, as are theplacental stem cells described herein, but remain attached to theadherent cells during culture. Embryoid-like body cells are dependentupon the adherent placental stem cells for viability, as embryoid-likebodies do not form in the absence of the adherent stem cells. Theadherent placental stem cells thus facilitate the growth of one or moreembryoid-like bodies in a population of placental cells that comprisethe adherent placental stem cells. Without wishing to be bound bytheory, the cells of the embryoid-like bodies are thought to grow on theadherent placental stem cells much as embryonic stem cells grow on afeeder layer of cells. Mesenchymal stem cells, e.g., bone marrow-derivedmesenchymal stem cells, do not develop embryoid-like bodies in culture.

5.2.5 Differentiation

The placental stem cells, useful in the methods provided herein, aredifferentiable into different committed cell lineages. For example, theplacental stem cells can be differentiated into cells of an hepatocyticlineage. Such differentiation can be accomplished, for example, by anymethod known in the art for differentiating, e.g., bone marrow-derivedmesenchymal stem cells into similar cell lineages. See U.S. patentapplication Ser. No. 11/648,813, filed Dec. 28, 2006, the disclosure ofwhich is hereby incorporated herein by reference in its entirety.

The placental stem cells to be differentiated can be contained in apolymer carrier, e.g., alginate. In one embodiment, provided herein is acomposition comprising a plurality of cells encapsulated in alginate.The cells can be placental stem cells, not contacted with conditionsthat cause differentiation of a placental stem cell into a hepatocyte ora hepatogenic cell. The cells can also be hepatogenic cells orhepatocytes. The cells can also be a combination of any of theforegoing. Hepatogenic cells and/or hepatocytes contained within thepolymer, e.g., alginate, are cells that are differentiated fromplacental stem cells. In one embodiment, said cells express at least onemarker of a hepatocyte not expressed by, or expressed to a detectablydifferent degree than, a placental stem cell. Preferably, the polymer,e.g., alginate, is in the form of beads that encapsulate a plurality ofplacental stem cells, hepatogenic cells, hepatocytes, or combinationthereof. The beads can vary in size. for example, the beads can varyfrom about (e.g., ±10%) 100 μm to about 1000 μm, between about In aspecific embodiment, said beads are from about 200 μm to about 800 μm insize. In another specific embodiment, said beads average about 500 μm insize.

5.3 CD34⁺CD45⁻ Placental Stem Cells and Cell Populations Comprising Them

In another aspect, provided herein are isolated hematopoietic CD34⁺,CD45⁻ placental stem cells and/or CD34⁺CD45^(dim) placental stem cells,and isolated populations of cells enriched in CD34⁺, CD45⁻ placentalstem cells. As used herein, “CD34⁺, CD45⁻ placental stem cell” indicatesa cell that is capable of differentiating into at least one type ofmature blood cell or progenitor of a mature blood cell, which isobtained from the placenta but not from placental or umbilical cordblood, and in certain embodiments includes CD34⁺CD45^(dim) placentalstem cells. The CD34⁺, CD45⁻ placental stem cell is detectably positivefor the marker CD34, e.g., using a labeled antibody to CD34, and is dimor negative for CD45, e.g., does not label with a fluorescently-labeledantibody to CD45 such that the cell is detectable above background.CD34⁺, CD45⁻ placental stem cells and CD34⁺CD45^(dim) placental stemcells placental stem cells are typically non-adherent, that is, they donot adhere to a tissue culture surface.

Also provided herein are populations of placental cells enriched forCD34⁺CD45⁻ placental stem cells and/or CD34⁺CD45^(dim) placental stemcells. As used herein, “enriched” indicates that the placental stem cellpopulation comprises a higher number or higher percentage of CD34⁺CD45⁻cells than is found in placental perfusate, when said placentalperfusate comprises about 750 mL of perfusion solution (e.g., 0.9% NaCl)passed through a human placenta at a rate of about 50 mL/min. after theplacenta has been drained of cord blood and placental blood andpre-perfused with about 100 mL of perfusion solution. In a specificembodiment, CD34⁺CD45⁻ placental stem cells are present in a cellpopulation at a higher percentage than found in placental perfusate,e.g., the placental stem cells constitute at least 1%, 2%, 3%, 4%, 5%,7%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 95% of the cellsin the cell population. In another specific embodiment, the stem cellpopulation comprises about, or at least, 1×10³, 5×10³, 1×10⁴, 5×10⁴,1×10⁵, 5×10⁵, 1×10⁶, 5×10⁶ or 1×10⁷ CD34⁺CD45⁻ placental stem cells.

Typically, from a population of about 100 million total nucleated cellsin placental perfusate, about 5% are CD34⁺ cells, and the final yieldfrom a placenta, taking into account viability, is about 1 million CD34⁺stem cells. CD34⁺ stem cells, when collected, appear round, with lowcellular complexity.

Populations of placental stem cells that comprise CD34⁺CD45⁻ placentalstem cells can also comprise other populations of CD34⁺ cells, forexample, CD34⁺CD38⁺ cells and/or CD34⁺CD38⁻ cells. In a specificembodiment, said CD34⁺CD38⁻ cells comprise CD34⁺CD38⁻lin⁻ stem cells. Inanother specific embodiment, said CD34⁺ placental stem cells comprisecells that are ALDH⁺, that is, CD34⁺, ALDH⁺ placental stem cells.

In another embodiment, CD34⁺, CD45⁻ placental stem cells are combinedwith stem cells of a second type. In one embodiment, the stem cells of asecond type comprises adherent placental stem cells that are OCT-4⁺ orABC-p⁺. In another more specific embodiment, said adherent placentalstem cells comprise cells that are OCT4⁺ABC-p⁺. In another more specificembodiment, said hematopoietic placental stem cells are contained withinplacental perfusate substantially lacking red blood cells and cellulardebris.

In another embodiment, the adherent placental stem cells, which arecombined with the hematopoietic placental stem cells, e.g., CD34 CD45⁻placental stem cells, comprise cells that express one or more of markersCD10, CD29, CD44, CD54, CD90, CD73 or CD105, and lack expression of oneor more of markers CD34, CD38, CD45, SSEA3 and SSEA4. In anotherembodiment, the adherent placental stem cells comprise cells that arepositive for CD10, CD29, CD44, CD54, CD90, CD73 or CD105, and negativefor CD34, CD38, CD45, SSEA3 and SSEA4. In another embodiment, theadherent placental stem cells comprise cells that comprise one or moreof markers CD10, CD29, CD44, CD54, CD90, CD73 and CD105, and lack one ormore of markers CD34, CD38, CD45, SSEA3 and SSEA4. In anotherembodiment, the adherent placental stem cells comprise cells that arepositive for CD10, CD29, CD44, CD54, CD90, CD73 and CD105, and negativefor CD34, CD38, CD45, SSEA3 and SSEA4. In another embodiment, theadherent placental stem cells comprise CD34⁻ cells. In a specificembodiment, the adherent placental stem cells are CD34⁻ CD38 placentalstem cells. In another embodiment, the adherent placental stem cellscomprise cells that are positive for at least one of CD10, CD29, CD33,CD44, CD73, CD105, CD117, and CD133, and negative for at least one ofCD34 or CD45. In another embodiment, the adherent placental stem cellscomprise cells that are positive for CD10, CD29, CD33, CD44, CD73,CD105, CD117, and CD133, and negative for CD34 or CD45. In a morespecific embodiment, the adherent placental stem cells comprise cellsthat are HLA-ABC⁺. In a more specific embodiment, the adherent placentalstem cells comprise cells that are HLA-ABC⁻. In a more specificembodiment, the adherent placental stem cells comprise cells that areHLA-DR⁺. In a more specific embodiment, the adherent placental stemcells comprise cells that are HLA-DR⁻. In another specific embodiment,the adherent placental stem cells comprise cells that are CD200⁺ orHLA-G⁺. In another specific embodiment, the adherent placental stemcells comprise cells that are CD200⁺ and IILA-G⁺. In another specificembodiment, the adherent placental stem cells comprise cells that areCD73⁺, CD105⁺ and CD200⁺. In another specific embodiment, the adherentplacental stem cells comprise cells that are CD200 and OCT-4⁺. Inanother specific embodiment, the adherent placental stem cells comprisecells that are CD73⁺, CD105⁺ and facilitate the formation ofembryoid-like bodies in a population of isolated placental cellscomprising said stem cells, when said population is cultured underconditions that allow the formation of embryoid-like bodies. In anotherspecific embodiment, the adherent placental stem cells comprise cellsthat are CD73⁺, CD105⁺ and HLA-G⁺. In another specific embodiment, theadherent placental stem cells comprise cells that are OCT-4⁺ andfacilitate the formation of embryoid-like bodies in a population ofisolated placental cells comprising said stem cells, when saidpopulation is cultured under conditions that allow the formation ofembryoid-like bodies.

In another embodiment, the second population of stem cells comprisescord blood stem cells and/or bone marrow stem cells.

CD34⁺CD45⁻ placental stem cells and other stem cells, to be combined,may be identically HLA-matched, that is, they may be derived from thesame individual. In another embodiment, the CD34⁺CD45⁻ placental stemcells and other stem cells may be HLA-mismatched, that is, they may bederived from different individuals. The combination of CD34⁺CD45⁻placental stem cells and other stem cells can comprise stem cells thatare either HLA-matched, partially HLA-matched, and/or HLA-mismatched toan intended recipient. For combined stem cell populations comprisingnon-cord blood stem cells, it is preferred that at least the stem cellsfrom a second source be HLA-matched or partially HLA-matched to anintended recipient.

In various embodiments, the ratio of CD34⁺CD45⁻ placental stem cells toa second type of stem cell can be about 100,000,000:1, 50,000,000:1,20,000,000:1, 10,000,000:1, 5,000,000:1, 2,000,000:1, 1,000,000:1,500,000:1, 200,000:1, 100,000:1, 50,000:1, 20,000:1, 10,000:1, 5,000:1,2,000:1, 1,000:1, 500:1, 200:1, 100:1, 50:1, 20:1, 10:1, 5:1, 2:1, 1:1;1:2; 1:5; 1:10; 1:100; 1:200; 1:500; 1:1,000; 1:2,000; 1:5,000;1:10,000; 1:20,000; 1:50,000; 1:100,000; 1:500,000; 1:1,000,000;1:2,000,000; 1:5,000,000; 1:10,000,000; 1:20,000,000; 1:50,000,000; orabout 1:100,000,000, comparing numbers of total nucleated cells in eachpopulation, or comparing total numbers of stem cells in each population.In various preferred embodiments, the ratio is about 1:10 to about 10:1,or is about 3:1 to about 1:3.

Further provided herein are populations of stem cells comprisingCD34⁺CD45⁻ placental stem cells and a second type of stem cell, whereinthe population of stem cells comprises a therapeutically-effectiveamount of CD34⁺CD45⁻ placental stem cells, second type of stem cell, orboth. In various combinations, the populations comprise at least 1×10⁴,5×10⁴, 1×10⁵, 5×10⁵, 1×10⁶, 5×10⁶, 1×10⁷, 5×10⁷, 1×10⁸, 5×10⁸, 1×10⁹,5×10⁹, 1×10¹⁰, 5×10¹⁰, or 1×10¹¹ CD34⁺CD45⁻ placental stem cells, secondtype of stem cell, or both, or no more than 1×10⁴, 5×10⁴, 1×10⁵, 5×10⁵,1×10⁶, 5×10⁶, 1×10⁷, 5×10⁷, 1×10⁸, 5×10⁸, 1×10⁹, 5×10⁹, 1×10¹⁰, 5×10¹⁰,or 1×10¹¹ CD34⁺CD45⁻ placental stem cells, second type of stem cells, orboth, or, alternatively, 3, 5, 10, 20, 30, 40, or 50 units or more, oftotal nucleated cells, from both the placental stem cell population andthe second type of stem cell.

5.4 Methods of Obtaining Placental Stem Cells

5.4.1 Stem Cell Collection Composition

The placental stem cells, e.g., adherent placental stem cells and/orCD34⁺, CD45⁻ placental stem cells, used in the methods and compositionsprovided herein can be collected by any means known in the art forcollecting cells from tissue, e.g., by perfusion of a placenta and/or byphysical and/or enzymatic disruption of placental tissue. Generally,stem cells are obtained from a mammalian placenta using aphysiologically-acceptable solution, e.g., a stem cell collectioncomposition. A stem cell collection composition is described in detailin related U.S. Application Publication No. 2007/0190042, entitled“Improved Composition for Collecting Placental Stem Cells and PreservingOrgans” filed on Dec. 28, 2006.

The stem cell collection composition can comprise anyphysiologically-acceptable solution suitable for the collection and/orculture of stem cells, for example, a saline solution (e.g.,phosphate-buffered saline, Kreb's solution, modified Kreb's solution,Eagle's solution, 0.9% NaCl. etc.), a culture medium (e.g., DMEM,H.DMEM, etc.), and the like.

The stem cell collection composition can comprise one or more componentsthat tend to preserve placental stem cells, that is, prevent theplacental stem cells from dying, or delay the death of the placentalstem cells, reduce the number of placental stem cells in a population ofcells that die, or the like, from the time of collection to the time ofculturing. Such components can be, e.g., an apoptosis inhibitor (e.g., acaspase inhibitor or JNK inhibitor); a vasodilator (e.g., magnesiumsulfate, an antihypertensive drug, atrial natriuretic peptide (ANP),adrenocorticotropin, corticotropin-releasing hormone, sodiumnitroprusside, hydralazine, adenosine triphosphate, adenosine,indomethacin or magnesium sulfate, a phosphodiesterase inhibitor, etc.);a necrosis inhibitor (e.g., 2-(1H-Indol-3-yl)-3-pentylamino-maleimide,pyrrolidine dithiocarbamate, or clonazepam); a TNF-α inhibitor; and/oran oxygen-carrying perfluorocarbon (e.g., perfluorooctyl bromide,perfluorodecyl bromide, etc.).

The stem cell collection composition can comprise one or moretissue-degrading enzymes, e.g., a metalloprotease, a serine protease, aneutral protease, a hyaluronidase, an RNase, or a DNase, or the like.Such enzymes include, but are not limited to, collagenases (e.g.,collagenase I, II, III or IV, a collagenase from Clostridiumhistolyticum, etc.); dispase, thennolysin, elastase, trypsin, LIBERASE,hyaluronidase, and the like.

The stem cell collection composition can comprise a bacteriocidally orbacteriostatically effective amount of an antibiotic. In certainnon-limiting embodiments, the antibiotic is a macrolide (e.g.,tobramycin), a cephalosporin (e.g., cephalexin, cephradine, cefuroxime,cefprozil, cefaclor, cefixime or cefadroxil), a clarithromycin, anerythromycin, a penicillin (e.g., penicillin V) or a quinolone (e.g.,ofloxacin, ciprofloxacin or norfloxacin), a tetracycline, astreptomycin, etc. In a particular embodiment, the antibiotic is activeagainst Gram(+) and/or Gram(−) bacteria, e.g., Pseudomonas aeruginosa,Staphylococcus aureus, and the like.

The stem cell collection composition can also comprise one or more ofthe following compounds: adenosine (about 1 mM to about 50 mM);D-glucose (about 20 mM to about 100 mM); magnesium ions (about 1 mM toabout 50 mM); a macromolecule of molecular weight greater than 20,000daltons, in one embodiment, present in an amount sufficient to maintainendothelial integrity and cellular viability (e.g., a synthetic ornaturally occurring colloid, a polysaccharide such as dextran or apolyethylene glycol present at about 25 g/l to about 100 g/l, or about40 g/l to about 60 g/l); an antioxidant (e.g., butylated hydroxyanisole,butylated hydroxytoluene, glutathione, vitamin C or vitamin E present atabout 25 μM to about 100 μM); a reducing agent (e.g., N-acetylcysteinepresent at about 0.1 mM to about 5 mM); an agent that prevents calciumentry into cells (e.g., verapamil present at about 2 μM to about 25 μM);nitroglycerin (e.g., about 0.05 g/L to about 0.2 g/L); an anticoagulant,in one embodiment, present in an amount sufficient to help preventclotting of residual blood (e.g., heparin or hirudin present at aconcentration of about 1000 units/1 to about 100,000 units/1); or anamiloride containing compound (e.g., amiloride, ethyl isopropylamiloride, hexamethylene amiloride, dimethyl amiloride or isobutylamiloride present at about 1.0 μM to about 5 μM).

5.4.2 Collection and Handling of Placenta

Generally, a human placenta is recovered shortly after its expulsionafter birth. In a preferred embodiment, the placenta is recovered from apatient after informed consent and after a complete medical history ofthe patient is taken and is associated with the placenta. Preferably,the medical history continues after delivery. Such a medical history canbe used to coordinate subsequent use of the placenta or the stem cellsharvested therefrom. For example, human placental stem cells can beused, in light of the medical history, for personalized medicine for theinfant associated with the placenta, or for parents, siblings or otherrelatives of the infant.

Prior to recovery of placental stem cells, the umbilical cord blood andplacental blood are removed. In certain embodiments, after delivery, thecord blood in the placenta is recovered. The placenta can be subjectedto a conventional cord blood recovery process. Typically a needle orcannula is used, with the aid of gravity, to exsanguinate the placenta(see, e.g., Anderson, U.S. Pat. No. 5,372,581; Hessel et al., U.S. Pat.No. 5,415,665). The needle or cannula is usually placed in the umbilicalvein and the placenta can be gently massaged to aid in draining cordblood from the placenta. Such cord blood recovery may be performedcommercially, e.g., LifebankUSA, Cedar Knolls, N.J.; ViaCord; Cord BloodRegistry; Cryocell; and the like. Preferably, the placenta is gravitydrained without further manipulation so as to minimize tissue disruptionduring cord blood recovery.

Typically, a placenta is transported from the delivery or birthing roomto another location, e.g., a laboratory, for recovery of cord blood andcollection of stem cells by, e.g., perfusion or tissue dissociation. Theplacenta is preferably transported in a sterile, thermally insulatedtransport device (maintaining the temperature of the placenta between20-28° C.), for example, by placing the placenta, with clamped proximalumbilical cord, in a sterile zip-lock plastic bag, which is then placedin an insulated container. In another embodiment, the placenta istransported in a cord blood collection kit substantially as described inU.S. Pat. No. 7,147,626 or in United States Patent ApplicationPublication No. 2006/0060494. Preferably, the placenta is delivered tothe laboratory four to twenty-four hours following delivery. In certainembodiments, the proximal umbilical cord is clamped, preferably within4-5 cm (centimeter) of the insertion into the placental disc prior tocord blood recovery. In other embodiments, the proximal umbilical cordis clamped after cord blood recovery but prior to further processing ofthe placenta.

The placenta, prior to stem cell collection, can be stored under sterileconditions and at either room temperature or at a temperature of 5 to25° C. (centigrade). The placenta may be stored for a period of longerthan forty eight hours, and preferably for a period of four totwenty-four hours prior to perfusing the placenta to remove any residualcord blood. The placenta is preferably stored in an anticoagulantsolution at a temperature of 5° C. to 25° C. (centigrade). Suitableanticoagulant solutions are well known in the art. For example, asolution of heparin or warfarin sodium can be used. In a preferredembodiment, the anticoagulant solution comprises a solution of heparin(e.g., 1% w/w in 1:1000 solution). The exsanguinated placenta ispreferably stored for no more than 36 hours before placental stem cellsare collected.

The mammalian placenta or a part thereof, once collected and preparedgenerally as above, can be treated in any art-known manner, e.g., can beperfused or disrupted, e.g., digested with one or more tissue-disruptingenzymes, to obtain stem cells.

5.4.3 Physical Disruption and Enzymatic Digestion of Placental Tissue

In one embodiment, stem cells are collected from a mammalian placenta byphysical disruption, e.g., enzymatic digestion, of the organ. Forexample, the placenta, or a portion thereof, may be, e.g., crushed,sheared, minced, diced, chopped, macerated or the like, while in contactwith the stem cell collection composition described herein, and thetissue subsequently digested with one or more enzymes. The placenta, ora portion thereof, may also be physically disrupted and digested withone or more enzymes, and the resulting material then immersed in, ormixed into, the stem cell collection composition described herein. Anymethod of physical disruption can be used, provided that the method ofdisruption leaves a plurality, more preferably a majority, and morepreferably at least 60%, 70%, 80%, 90%, 95%, 98%, or 99% of the cells insaid organ viable, as determined by, e.g., trypan blue exclusion.

The placenta can be dissected into components prior to physicaldisruption and/or enzymatic digestion and stem cell recovery. Forexample, placental stem cells can be obtained from all or a portion ofthe amniotic membrane, chorion, placental cotyledons, or any combinationthereof. Preferably, placental stem cells are obtained from placentaltissue comprising amnion and chorion. Typically, placental stem cellscan be obtained by disruption of a small block of placental tissue,e.g., a block of placental tissue that is about 1, 2, 3, 4, 5, 6, 7, 8,9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600,700, 800, 900 or about 1000 cubic millimeters in volume.

A preferred stem cell collection composition comprises one or moretissue-disruptive enzyme(s). Enzymatic digestion preferably uses acombination of enzymes, e.g., a combination of a matrix metalloproteaseand a neutral protease, for example, a combination of collagenase anddispase. In one embodiment, enzymatic digestion of placental tissue usesa combination of a matrix metalloprotease, a neutral protease, and amucolytic enzyme for digestion of hyaluronic acid, such as a combinationof collagenase, dispase, and hyaluronidase or a combination of LIBERASE(Boehringer Mannheim Corp., Indianapolis, Ind.) and hyaluronidase. Otherenzymes that can be used to disrupt placenta tissue include papain,deoxyribonucleases, serine proteases, such as trypsin, chymotrypsin, orelastase. Serine proteases may be inhibited by alpha 2 microglobulin inserum and therefore the medium used for digestion is usually serum-free.EDTA and DNase are commonly used in enzyme digestion procedures toincrease the efficiency of cell recovery. The digestate is preferablydiluted so as to avoid trapping stem cells within the viscous digest.

Any combination of tissue digestion enzymes can be used. Typicalconcentrations for tissue digestion enzymes include, e.g., 50-200 U/mLfor collagenase I and collagenase IV, 1-10 U/mL for dispase, and 10-100U/mL for elastase. Proteases can be used in combination, that is, two ormore proteases in the same digestion reaction, or can be usedsequentially in order to liberate placental stem cells. For example, inone embodiment, a placenta, or part thereof, is digested first with anappropriate amount of collagenase I at 2 mg/ml for 30 minutes, followedby digestion with trypsin, 0.25%, for 10 minutes, at 37° C. Scrineproteases are preferably used consecutively following use of otherenzymes.

In another embodiment, the tissue can further be disrupted by theaddition of a chelator, e.g., ethylene glycol bis(2-aminoethylether)-N,N,N′N′-tetraacetic acid (EGTA) or ethylenediaminetetraaceticacid (EDTA) to the stein cell collection composition comprising the stemcells, or to a solution in which the tissue is disrupted and/or digestedprior to isolation of the stem cells with the stem cell collectioncomposition.

It will be appreciated that where an entire placenta, or portion of aplacenta comprising both fetal and maternal cells (for example, wherethe portion of the placenta comprises the chorion or cotyledons), theplacental stem cells collected will comprise a mix of placental stemcells derived from both fetal and maternal sources. Where a portion ofthe placenta that comprises no, or a negligible number of, maternalcells (for example, amnion), the placental stem cells collected willcomprise almost exclusively fetal placental stem cells.

5.4.4 Placental Perfusion

Placental stem cells useful in the methods and compositions providedherein can also be obtained by perfusion of the mammalian placenta.Methods of perfusing mammalian placenta to obtain stem cells aredisclosed, e.g., in Hariri, U.S. Pat. Nos. 7,045,148 and 7,255,879, andin U.S. Application Publication No. 2007/0190042, entitled “ImprovedComposition for Collecting and Preserving Organs.”

Placental stem cells can be collected by perfusion, e.g., through theplacental vasculature, using, e.g., a stem cell collection compositionas a perfusion solution. In one embodiment, a mammalian placenta isperfused by passage of perfusion solution through either or both of theumbilical artery and umbilical vein. The flow of perfusion solutionthrough the placenta may be accomplished using, e.g., gravity flow intothe placenta. Preferably, the perfusion solution is forced through theplacenta using a pump, e.g., a peristaltic pump. The umbilical vein canbe, e.g., cannulated with a cannula, e.g., a TEFLON® or plastic cannula,that is connected to a sterile connection apparatus, such as steriletubing. The sterile connection apparatus is connected to a perfusionmanifold.

In preparation for perfusion, the placenta is preferably oriented (e.g.,suspended) in such a manner that the umbilical artery and umbilical veinare located at the highest point of the placenta. The placenta can beperfused by passage of a perfusion fluid, e.g., a stem cell collectioncomposition as provided herein, through the placental vasculature, orthrough the placental vasculature and surrounding tissue. In oneembodiment, the umbilical artery and the umbilical vein are connectedsimultaneously to a pipette that is connected via a flexible connectorto a reservoir of the perfusion solution. The perfusion solution ispassed into the umbilical vein and artery. The perfusion solution exudesfrom and/or passes through the walls of the blood vessels into thesurrounding tissues of the placenta, and is collected in a suitable openvessel from the surface of the placenta that was attached to the uterusof the mother during gestation. The perfusion solution may also beintroduced through the umbilical cord opening and allowed to flow orpercolate out of openings in the wall of the placenta which interfacedwith the maternal uterine wall. In another embodiment, the perfusionsolution is passed through the umbilical veins and collected from theumbilical artery, or is passed through the umbilical artery andcollected from the umbilical veins, that is, is passed through only theplacental vasculature (fetal tissue). This can be referred to as the“closed circuit” method of perfusion. The closed circuit perfusionmethod can, in one embodiment, be performed as follows. A post-partumplacenta is obtained within about 48 hours after birth. The umbilicalcord is clamped and cut above the clamp. The umbilical cord can bediscarded, or can processed to recover, e.g., umbilical cord stem cells,and/or to process the umbilical cord membrane for the production of abiomaterial. The amniotic membrane can be retained during perfusion, orcan be separated from the chorion, e.g., using blunt dissection with thefingers. If the amniotic membrane is separated from the chorion prior toperfusion, it can be, e.g., discarded, or processed, e.g., to obtainstem cells by enzymatic digestion, or to produce, e.g., an amnioticmembrane biomaterial, e.g., the biomaterial described in U.S.Application Publication No. 2004/0048796. After cleaning the placenta ofall visible blood clots and residual blood, e.g., using sterile gauze,the umbilical cord vessels are exposed, e.g., by partially cutting theumbilical cord membrane to expose a cross-section of the cord. Thevessels are identified, and opened, e.g., by advancing a closedalligator clamp through the cut end of each vessel. The apparatus, e.g.,plastic tubing connected to a perfusion device or peristaltic pump, isthen inserted into each of the placental arteries. The pump can be anypump suitable for the purpose, e.g., a peristaltic pump. Plastic tubing,connected to a sterile collection reservoir, e.g., a blood bag such as a250 mL collection bag, is then inserted into the placental vein.Alternatively, the tubing connected to the pump is inserted into theplacental vein, and tubes to a collection reservoir(s) are inserted intoone or both of the placental arteries. The placenta is then perfusedwith a volume of perfusion solution, e.g., about 750 ml of perfusionsolution. Cells in the perfusate are then collected, e.g., bycentrifugation.

In one embodiment, the proximal umbilical cord is clamped duringperfusion, and more preferably, is clamped within 4-5 cm (centimeter) ofthe cord's insertion into the placental disc.

The first collection of perfusion fluid from a mammalian placenta duringthe exsanguination process is generally colored with residual red bloodcells of the cord blood and/or placental blood. The perfusion fluidbecomes more colorless as perfusion proceeds and the residual cord bloodcells are washed out of the placenta. Generally from 30 to 100 mL ofperfusion fluid is adequate to initially exsanguinate the placenta, butmore or less perfusion fluid may be used depending on the observedresults.

The volume of perfusion liquid used to collect placental stem cells mayvary depending upon the number of stem cells to be collected, the sizeof the placenta, the number of collections to be made from a singleplacenta, etc. In various embodiments, the volume of perfusion liquidmay be from 50 mL to 5000 mL, 50 mL to 4000 mL, 50 mL to 3000 mL, 100 mLto 2000 mL, 250 mL to 2000 mL, 500 mL to 2000 mL, or 750 mL to 2000 mL.Typically, the placenta is perfused with 700-800 mL of perfusion liquidfollowing exsanguination.

The placenta can be perfused a plurality of times over the course ofseveral hours or several days. Where the placenta is to be perfused aplurality of times, it may be maintained or cultured under asepticconditions in a container or other suitable vessel, and perfused withthe stem cell collection composition, or a standard perfusion solution(e.g., a normal saline solution such as phosphate buffered saline(“PBS”) with or without an anticoagulant (e.g., heparin, warfarinsodium, coumarin, bishydroxycotunarin), and/or with or without anantimicrobial agent (e.g., β-mercaptoethanol (0.1 mM); antibiotics suchas streptomycin (e.g., at 40-100 μg/ml), penicillin (e.g., at 40 U/ml),amphotericin B (e.g., at 0.5 μg/ml). In one embodiment, an isolatedplacenta is maintained or cultured for a period of time withoutcollecting the perfusate, such that the placenta is maintained orcultured for 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,18, 19, 20, 21, 22, 23, or 24 hours, or 2 or 3 or more days beforeperfusion and collection of perfusate. The perfused placenta can bemaintained for one or more additional time(s), e.g., 1, 2, 3, 4, 5, 6,7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 ormore hours, and perfused a second time with, e.g., 700-800 mL perfusionfluid. The placenta can be perfused 1, 2, 3, 4, 5 or more times, forexample, once every 1, 2, 3, 4, 5 or 6 hours. In a preferred embodiment,perfusion of the placenta and collection of perfusion solution, e.g.,stem cell collection composition, is repeated until the number ofrecovered nucleated cells falls below 100 cells/ml. The perfusates atdifferent time points can be further processed individually to recovertime-dependent populations of cells, e.g., stem cells. Perfusates fromdifferent time points can also be pooled.

Without wishing to be bound by any theory, after exsanguination and asufficient time of perfusion of the placenta, placental stem cells arebelieved to migrate into the exsanguinated and perfused microcirculationof the placenta where, according to the methods described herein, theyare collected, preferably by washing into a collecting vessel byperfusion. Perfusing the isolated placenta not only serves to removeresidual cord blood but also provide the placenta with the appropriatenutrients, including oxygen. The placenta may be cultivated and perfusedwith a similar solution which was used to remove the residual cord bloodcells, preferably, without the addition of anticoagulant agents.

Perfusion according to the methods described herein typically results inthe collection of significantly more placental stem cells than thenumber obtainable from a mammalian placenta not perfused with saidsolution, and not otherwise treated to obtain stem cells (e.g., bytissue disruption, e.g., enzymatic digestion). In this context,“significantly more” means at least 10% more. Perfusion as describedherein yields significantly more placental stem cells than, e.g., thenumber of placental stem cells obtainable from culture medium in which aplacenta, or portion thereof, has been cultured.

Stem cells can be isolated from placenta by perfusion with a solutioncomprising one or more proteases or other tissue-disruptive enzymes. Ina specific embodiment, a placenta or portion thereof (e.g., amnioticmembrane, amnion and chorion, placental lobule or cotyledon, orcombination of any of the foregoing) is brought to 25-37° C., and isincubated with one or more tissue-disruptive enzymes in 200 mL of aculture medium for 30 minutes. Cells from the perfusate are collected,brought to 4° C., and washed with a cold inhibitor mix comprising 5 mMEDTA, 2 mM dithiothreitol and 2 mM beta-mercaptoethanol. The stem cellsare washed after several minutes with a cold (e.g., 4° C.) stem cellcollection composition.

It will be appreciated that perfusion using the pan method, that is,whereby perfusate is collected after it has exuded from the maternalside of the placenta, results in a mix of fetal and maternal cells. As aresult, the cells collected by this method comprise a mixed populationof placental stem cells of both fetal and maternal origin. In contrast,perfusion solely through the placental vasculature, whereby perfusionfluid is passed through one or two placental vessels and is collectedsolely through the remaining vessel(s), results in the collection of apopulation of placental stem cells almost exclusively of fetal origin.

5.4.5 Isolation, Sorting, and Characterization of Placental Stem Cells

1 Stem cells from mammalian placenta, whether obtained by perfusion orenyzmatic digestion, can initially be purified from (i.e., be isolatedfrom) other cells by Ficoll gradient centrifugation. Such centrifugationcan follow any standard protocol for centrifugation speed, etc. In oneembodiment, for example, cells collected from the placenta are recoveredfrom perfusate by centrifugation at 5000×g for 15 minutes at roomtemperature, which separates cells from, e.g., contaminating debris andplatelets. In another embodiment, placental perfusate is concentrated toabout 200 ml, gently layered over Ficoll, and centrifuged at about1100×g for 20 minutes at 22° C., and the low-density interface layer ofcells is collected for further processing.

Cell pellets can be resuspended in fresh stem cell collectioncomposition, or a medium suitable for stem cell maintenance, e.g., IMDMserum-free medium containing 2 U/ml heparin and 2 mM EDTA (GibcoBRL,NY). The total mononuclear cell fraction can be isolated, e.g., usingLYMPHOPREP™ (Nycomed Pharma, Oslo, Norway) according to themanufacturer's recommended procedure.

As used herein, “isolating” placental stem cells means to remove atleast 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95% or 99% of the cellswith which the stem cells are normally associated in the intactmammalian placenta. A stem cell from an organ is “isolated” when it ispresent in a population of cells that comprises fewer than 50% of thecells with which the stem cell is normally associated in the intactorgan.

Placental cells obtained by perfusion or digestion can, for example, befurther, or initially, isolated by differential trypsinization using,e.g., a solution of 0.05% trypsin with 0.2% EDTA (Sigma, St. Louis Mo.).Differential trypsinization is possible because placental stem cellstypically detach from plastic surfaces within about five minutes whereasother adherent populations typically require more than 20-30 minutesincubation. The detached placental stem cells can be harvested followingtrypsinization and trypsin neutralization, using, e.g., TrypsinNeutralizing Solution (TNS, Cambrex). In one embodiment of isolation ofadherent cells, aliquots of, for example, about 5-10×10⁶ cells areplaced in each of several T-75 flasks, preferably fibronectin-coated T75flasks. In such an embodiment, the cells can be cultured withcommercially available Mesenchymal Stem Cell Growth Medium (MSCGM™)(Cambrex), and placed in a tissue culture incubator (37° C., 5% CO₂).After 10 to 15 days, non-adherent cells are removed from the flasks bywashing with PBS. The PBS is then replaced by MSCGM™. Flasks arepreferably examined daily for the presence of various adherent celltypes and in particular, for identification and expansion of clusters offibroblastoid cells.

The number and type of cells collected from a mammalian placenta can bemonitored, for example, by measuring changes in morphology and cellsurface markers using standard cell detection techniques such as flowcytometry, cell sorting, immunocytochemistry (e.g., staining with tissuespecific or cell-marker specific antibodies) fluorescence activated cellsorting (FACS), magnetic activated cell sorting (MACS), by examinationof the morphology of cells using light or confocal microscopy, and/or bymeasuring changes in gene expression using techniques well known in theart, such as PCR and gene expression profiling. These techniques can beused, too, to identify cells that are positive for one or moreparticular markers. For example, using antibodies to CD34, one candetermine, using the techniques above, whether a cell comprises adetectable amount of CD34; if so, the cell is CD34⁺. Likewise, if a cellproduces enough OCT-4 RNA to be detectable by RT-PCR, or significantlymore OCT-4 RNA than an adult cell, the cell is OCT-4⁺ Antibodies to cellsurface markers (e.g., CD markers such as CD34) and the sequence of stemcell-specific genes, such as OCT-4, are well-known in the art.

Placental cells, particularly cells that have been isolated by Ficollseparation, differential adherence, or a combination of both, may besorted using a fluorescence activated cell sorter (FACS). Fluorescenceactivated cell sorting (FACS) is a well-known method for separatingparticles, including cells, based on the fluorescent properties of theparticles (Kamarch, 1987, Methods Enzymol, 151:150-165). Laserexcitation of fluorescent moieties in the individual particles resultsin a small electrical charge allowing electromagnetic separation ofpositive and negative particles from a mixture. In one embodiment, cellsurface marker-specific antibodies or ligands are labeled with distinctfluorescent labels. Cells are processed through the cell sorter,allowing separation of cells based on their ability to bind to theantibodies used. FACS sorted particles may be directly deposited intoindividual wells of 96-well or 384-well plates to facilitate separationand cloning.

In one sorting scheme, stem cells from placenta are sorted on the basisof expression of the markers CD34, CD38, CD44, CD45, CD73, CD105, CD117,CD200, OCT-4 and/or HLA-G. This can be accomplished in connection withprocedures to select stem cells on the basis of their adherenceproperties in culture. For example, an adherence selection stem can beaccomplished before or after sorting on the basis of marker expression.In one embodiment, for example, cells are sorted first on the basis oftheir expression of CD34; CD34⁻ cells are retained, and cells that areCD200⁺HLA-G⁺ are separated from all other CD34⁻ cells. In anotherembodiment, cells from placenta are based on their expression of markersCD200 and/or HLA-G; for example, cells displaying either of thesemarkers are isolated for further use. Cells that express, e.g., CD200and/or HLA-G can, in a specific embodiment, be further sorted based ontheir expression of CD73 and/or CD105, or epitopes recognized byantibodies SH2, SH3 or SH4, or lack of expression of CD34, CD38 or CD45.For example, in one embodiment, placental cells are sorted byexpression, or lack thereof, of CD200, HLA-G, CD73, CD105, CD34, CD38and CD45, and placental cells that are CD200⁺, HLA-G⁺, CD73⁺, CD105⁺,CD34⁻, CD38⁻ and CD45⁻ are isolated from other placental cells forfurther use.

With respect to antibody-mediated detection and sorting of placentalstem cells, any antibody, specific for a particular marker, can be used,in combination with any fluorophore or other label suitable for thedetection and sorting of cells (e.g., fluorescence-activated cellsorting). Antibody/fluorophore combinations to specific markers include,but are not limited to, fluorescein isothiocyanate (FITC) conjugatedmonoclonal antibodies against HLA-G (available from Serotec, Raleigh,N.C.), CD10 (available from BD Immunocytometry Systems, San Jose,Calif.), CD44 (available from BD Biosciences Pharmingen, San Jose,Calif.), and CD105 (available from R&D Systems Inc., Minneapolis,Minn.); phycoerythrin (PE) conjugated monoclonal antibodies againstCD44, CD200, CD117, and CD13 (BD Biosciences Pharmingen);phycoerythrin-Cy7 (PE Cy7) conjugated monoclonal antibodies against CD33and CD10 (BD Biosciences Pharmingen); allophycocyanin (APC) conjugatedstreptavidin and monoclonal antibodies against CD38 (BD BiosciencesPharmingen); and Biotinylated CD90 (BD Biosciences Pharmingen). Otherantibodies that can be used include, but are not limited to, CD133⁻ APC(Miltenyi), KDR-Biotin (CD309, Abcam), CytokeratinK-Fitc (Sigma orDako), HLA ALC-Fitc (BD), HLA DRDQDP-PE (BD), β-2-microglobulin-PE (BD),CD80⁻ PE (BD) and CD86⁻ APC (BD).

Other antibody/label combinations that can be used include, but are notlimited to, CD45⁻ PerCP (peridin chlorophyll protein); CD44⁻ PE; CD19⁻PE; CD10⁻ F (fluorescein); HLA-G-F and 7-amino-actinomycin-D (7-AAD);HLA-ABC-F; and the like.

Placental stem cells can be assayed for CD117 or CD133 using, forexample, phycoerythrin-Cy5 (PE Cy5) conjugated streptavidin and biotinconjugated monoclonal antibodies against CD117 or CD133; however, usingthis system, the cells can appear to be positive for CD117 or CD133,respectively, because of a relatively high background.

Placental stem cells can be labeled with an antibody to a single markerand detected and/sorted. Placental stem cells can also be simultaneouslylabeled with multiple antibodies to different markers.

In another embodiment, magnetic beads can be used to separate cells. Thecells may be sorted using a magnetic activated cell sorting (MACS)technique, a method for separating particles based on their ability tobind magnetic beads (0.5-100 μm diameter). A variety of usefulmodifications can be performed on the magnetic microspheres, includingcovalent addition of antibody that specifically recognizes a particularcell surface molecule or hapten. The beads are then mixed with the cellsto allow binding. Cells are then passed through a magnetic field toseparate out cells having the specific cell surface marker. In oneembodiment, these cells can then isolated and re-mixed with magneticbeads coupled to an antibody against additional cell surface markers.The cells are again passed through a magnetic field, isolating cellsthat bound both the antibodies. Such cells can then be diluted intoseparate dishes, such as microtiter dishes for clonal isolation.

Placental stem cells can also be characterized and/or sorted based oncell morphology and growth characteristics. For example, placental stemcells can be characterized as having, and/or selected on the basis of,e.g., a fibroblastoid appearance in culture. Placental stem cells canalso be characterized as having, and/or be selected, on the basis oftheir ability to form embryoid-like bodies. In one embodiment, forexample, placental cells that are fibroblastoid in shape, express CD73and CD105, and produce one or more embryoid-like bodies in culture areisolated from other placental cells. In another embodiment, OCT-4⁺placental cells that produce one or more embryoid-like bodies in cultureare isolated from other placental cells.

In another embodiment, placental stem cells can be identified andcharacterized by a colony forming unit assay. Colony forming unit assaysare commonly known in the art, such as MESENCULT® medium (Stem CellTechnologies, Inc., Vancouver British Columbia)

Placental stem cells can be assessed for viability, proliferationpotential, and longevity using standard techniques known in the art,such as trypan blue exclusion assay, fluorescein diacetate uptake assay,propidium iodide uptake assay (to assess viability); and thymidineuptake assay, MTT cell proliferation assay (ATCC; to assessproliferation). Longevity may be determined by methods well known in theart, such as by determining the maximum number of population doubling inan extended culture.

Placental stem cells can also be separated from other placental cellsusing other techniques known in the art, e.g., selective growth ofdesired cells (positive selection), selective destruction of unwantedcells (negative selection); separation based upon differential cellagglutinability in the mixed population as, for example, with soybeanagglutinin; freeze-thaw procedures; filtration; conventional and zonalcentrifugation; centrifugal elutriation (counter-streamingcentrifugation); unit gravity separation; countercurrent distribution;electrophoresis; and the like.

5.5 Culture of Placental Stem Cells

5.5.1 Culture Media

Isolated placental stem cells, or placental stem cell population, orcells or placental tissue from which placental stem cells grow out, canbe used to initiate, or seed, cell cultures. Cells are generallytransferred to sterile tissue culture vessels either uncoated or coatedwith extracellular matrix or ligands such as laminin, collagen (e.g.,native or denatured), gelatin, fibronectin, ornithine, vitronectin, andextracellular membrane protein (e.g., MATRIGEL (BD Discovery Labware,Bedford, Mass.)).

Placental stem cells can be cultured in any medium, and under anyconditions, recognized in the art as acceptable for the culture of stemcells. Preferably, the culture medium comprises serum. Placental stemcells can be cultured in, for example, DMEM-LG (Dulbecco's ModifiedEssential Medium, low glucose)/MCDB 201 (chick fibroblast basal medium)containing ITS (insulin-transferrin-selenium), LA+BSA (linoleicacid-bovine serum albumin), dextrose, L-ascorbic acid, PDGF, EGF, IGF-1,and penicillin/streptomycin; DMEM-HG (high glucose) comprising 10% fetalbovine serum (FBS); DMEM-HG comprising 15% FBS; IMDM (Iscove's modifiedDulbecco's medium) comprising 10% FBS, 10% horse serum, andhydrocortisone; M199 comprising 10% FBS, EGF, and heparin; α-MEM(minimal essential medium) comprising 10% FBS, GLUTAMAX™ and gentamicin;DMEM comprising 10% FBS, GLUTAMAX™ and gentamicin, etc. A preferredmedium is DMEM-LG/MCDB-201 comprising 2% FBS, ITS, LA+BSA, dextrose,L-ascorbic acid, PDGF, EGF, and penicillin/streptomycin.

Other media that can be used to culture placental stem cells includeDMEM (high or low glucose), Eagle's basal medium, Ham's F10 medium(F10), Ham's F-12 medium (F12), Iscove's modified Dulbecco's medium,Mesenchymal Stem Cell Growth Medium (MSCGM), Liebovitz's L-15 medium,MCDB, DMEM/F12, RPMI 1640, advanced DMEM (Gibco), DMEM/MCDB201 (Sigma),and CELLGRO FREE™.

The culture medium can be supplemented with one or more componentsincluding, for example, serum (e.g., fetal bovine serum (FBS),preferably about 2-15% (v/v); equine (horse) serum (ES); human serum(HIS)); beta-mercaptoethanol (BME), preferably about 0.001% (v/v); oneor more growth factors, for example, platelet-derived growth factor(PDGF), epidermal growth factor (EGF), basic fibroblast growth factor(bFGF), insulin-like growth factor-1 (IGF-1), leukemia inhibitory factor(LIF), vascular endothelial growth factor (VEGF), and erythropoietin(EPO); amino acids, including L-valine; one or more antibiotic and/orantimycotic agents to control microbial contamination, such as, forexample, penicillin G, streptomycin sulfate, amphotericin B, gentamicin,and nystatin, either alone or in combination; and one or moreneuroectoderm specification factors, for example, sonic hedgehog (shh)and/or retinoic acid (ra).

Placental stem cells can be cultured in standard tissue cultureconditions, e.g., in tissue culture dishes or multiwell plates.Placental stem cells can also be cultured using a hanging drop method.In this method, placental stem cells are suspended at about 1×10⁴ cellsper mL in about 5 mL of medium, and one or more drops of the medium areplaced on the inside of the lid of a tissue culture container, e.g., a100 mL Petri dish. The drops can be, e.g., single drops, or multipledrops from, e.g., a multichannel pipetter. The lid is carefully invertedand placed on top of the bottom of the dish, which contains a volume ofliquid, e.g., sterile PBS sufficient to maintain the moisture content inthe dish atmosphere, and the stem cells are cultured.

In one embodiment, the placental stem cells are cultured in the presenceof a compound that acts to maintain an undifferentiated phenotype in theplacental stem cell. In a specific embodiment, the compound is asubstituted 3,4-dihydropyridimol[4,5-d]pyrimidine. In a more specificembodiment, the compound is a compound having the following chemicalstructure:

The compound can be contacted with a placental stem cell, or populationof placental stem cells, at a concentration of, for example, betweenabout 1 μM to about 10 μM.

5.5.2 Expansion and Proliferation of Placental Stem Cells

Once an isolated placental stem cell, or isolated population of stemcells (e.g., a stem cell or population of stem cells separated from atleast 50% of the placental cells with which the stem cell or populationof stem cells is normally associated in vivo), the stem cell orpopulation of stem cells can be proliferated and expanded in vitro. Forexample, a population of placental stem cells can be cultured in tissueculture containers, e.g., dishes, flasks, multiwell plates, or the like,for a sufficient time for the stem cells to proliferate to 70-90%confluence, that is, until the stem cells and their progeny occupy70-90% of the culturing surface area of the tissue culture container.

Placental stem cells can be seeded in culture vessels at a density thatallows cell growth. For example, the cells may be seeded at low density(e.g., about 1,000 to about 5,000 cells/cm²) to high density (e.g.,about 50,000 or more cells/cm²). In a preferred embodiment, the cellsare cultured at about 0 to about 5 percent by volume CO₂ in air. In somepreferred embodiments, the cells are cultured at about 2 to about 25percent O₂ in air, preferably about 5 to about 20 percent O₂ in air. Thecells preferably are cultured at about 25° C. to about 40° C.,preferably 37° C. The cells are preferably cultured in an incubator. Theculture medium can be static or agitated, for example, using abioreactor. Placental stem cells preferably are grown under lowoxidative stress (e.g., with addition of glutathione, ascorbic acid,catalase, tocopherol, N-acetylcysteine, or the like).

Once 70%-90% confluence is obtained, the cells may be passaged. Forexample, the cells can be enzymatically treated, e.g., trypsinized,using techniques well-known in the art, to separate them from the tissueculture surface. After removing the cells by pipetting and counting thecells, about 20,000-100,000 stem cells, preferably about 50,000 stemcells, are passaged to a new culture container containing fresh culturemedium. Typically, the new medium is the same type of medium from whichthe stem cells were removed. Also provided herein are populations ofplacental stem cells that have been passaged at least 1, 2, 3, 4, 5, 6,7, 8, 9, 10, 12, 14, 16, 18, or 20 times, or more.

5.5.3 Placental Stem Cell Populations

In one aspect, placental stem cells and populations of placental stemcells are used as a source of differentiated cells, e.g., hepatocytesand/or hepatogenic cells, or chondrocytes and/or chondrogenic cells.Placental stem cell populations can be isolated directly from one ormore placentas; that is, the placental stem cell population can be apopulation of placental cells, comprising placental stem cells, obtainedfrom, or contained within, perfusate, or obtained from, or containedwithin, digestate (that is, the collection of cells obtained byenzymatic digestion of a placenta or part thereof). Isolated placentalstem cells described herein can also be cultured and expanded to produceplacental stem cell populations. Populations of placental cellscomprising placental stem cells can also be cultured and expanded toproduce placental stem cell populations.

Placental stem cell populations provided herein comprise placental stemcells, for example, placental stem cells as described herein. In variousembodiments, at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%,or 99% of the cells in an isolated placental stem cell population areplacental stem cells. That is, a placental stem cell population cancomprise, e.g., as much as 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%,80%, 90% non-stem cells.

Further provided herein are methods of producing isolated placental stemcell population by, e.g., selecting placental stem cells, whetherderived from enzymatic digestion or perfusion, that express particularmarkers and/or particular culture or morphological characteristics. Suchplacental stem cells can be used to produce, e.g., hepatocytes and/orhepatogenic cells, or mixed populations of undifferentiated placentalstem cells and hepatogenic cells and/or hepatocytes differentiated fromplacental stem cells; or chondrocytes and/or chondrogenic cells, ormixed populations of undifferentiated placental stem cells andchondrocytes and/or chondrogenic cells.

Cell populations comprising placental stem cells can be produced in avariety of different ways. In one embodiment, for example, a cellpopulation comprising placental stem cells can be produced by selectingplacental cells that (a) adhere to a substrate, and (b) express CD200and HLA-G; and isolating said cells from other cells to form a cellpopulation. In another embodiment, the method of producing a cellpopulation comprises selecting placental cells that (a) adhere to asubstrate, and (b) express CD73, CD105, and CD200; and isolating saidcells from other cells to form a cell population. In another embodiment,the method of producing a cell population comprises selecting placentalcells that (a) adhere to a substrate and (b) express CD200 and OCT-4;and isolating said cells from other cells to form a cell population. Inanother embodiment, the method of producing a cell population comprisesselecting placental cells that (a) adhere to a substrate, (b) expressCD73 and CD105, and (c) facilitate the formation of one or moreembryoid-like bodies in a population of placental cells comprising saidstem cell when said population is cultured under conditions that allowfor the formation of an embryoid-like body; and isolating said cellsfrom other cells to form a cell population. In another embodiment, themethod of producing a cell population comprises selecting placentalcells that (a) adhere to a substrate, and (b) express CD73, CD105 andHLA-G; and isolating said cells from other cells to form a cellpopulation. In another embodiment, the method of producing a cellpopulation comprises selecting placental cells that (a) adhere to asubstrate, (b) express OCT-4, and (c) facilitate the formation of one ormore embryoid-like bodies in a population of placental cells comprisingsaid stem cell when said population is cultured under conditions thatallow for the formation of an embryoid-like body; and isolating saidcells from other cells to form a cell population. In any of the aboveembodiments, the method can additionally comprise selecting placentalcells that express ABC-p (a placenta-specific ABC transporter protein;see, e.g., Allikmets et al., Cancer Res. 58(23):5337-9 (1998)). Themethod can also comprise selecting cells exhibiting at least onecharacteristic specific to, e.g., a mesenchymal stem cell, for example,expression of CD29, expression of CD44, expression of CD90, orexpression of a combination of the foregoing.

In any of the above embodiments of producing a cell population, theresulting population of cells can be additionally assessed for theability of the cells, or of the population, to produce, e.g.,hepatocytes, hepatogenic cells, chondrocytes, or chondrocytic cells.

In the above embodiments, the substrate can be any surface on whichculture and/or selection of cells, e.g., placental stem cells, can beaccomplished. Typically, the substrate is plastic, e.g., tissue culturedish or multiwell plate plastic. Tissue culture plastic can be coatedwith a biomolecule, e.g., laminin or fibronectin.

Cells, e.g., placental stem cells, can be selected for a placental stemcell population by any means known in the art of cell selection. Forexample, cells can be selected using an antibody or antibodies to one ormore cell surface markers, for example, in flow cytometry or FACS.Selection can be accomplished using antibodies in conjunction withmagnetic beads. Antibodies that are specific for certain stemcell-related markers are known in the art. For example, antibodies toOCT-4 (Abcam, Cambridge, Mass.), CD200 (Abcam), HLA-G (Abcam), CD73 (BDBiosciences Pharmingen, San Diego, Calif.), CD105 (Abcam; BioDesignInternational, Saco, Me.), etc. Antibodies to other markers are alsoavailable commercially, e.g., CD34, CD38 and CD45 are available from,e.g., StemCell Technologies or BioDesign International.

The isolated placental stem cell population can comprise placental cellsthat are not stem cells, or cells that are not placental cells.

Isolated placental stem cell populations can be combined with one ormore populations of non-stem cells or non-placental cells. For example,an isolated population of placental stem cells can be combined withblood (e.g., placental blood or umbilical cord blood), blood-derivedstem cells (e.g., stem cells derived from placental blood or umbilicalcord blood), populations of blood-derived nucleated cells, bonemarrow-derived mesenchymal cells, bone-derived stem cell populations,crude bone marrow, adult (somatic) stem cells, populations of stem cellscontained within tissue, cultured stem cells, populations offully-differentiated cells (e.g., chondrocytes, fibroblasts, amnioticcells, osteoblasts, muscle cells, cardiac cells, etc.) and the like.Cells in an isolated placental stem cell population can be combined witha plurality of cells of another type in ratios of about 100,000,000:1,50,000,000:1, 20,000,000:1, 10,000,000:1, 5,000,000:1, 2,000,000:1,1,000,000:1, 500,000:1, 200,000:1, 100,000:1, 50,000:1, 20,000:1,10,000:1, 5,000:1, 2,000:1, 1,000:1, 500:1, 200:1, 100:1, 50:1, 20:1,10:1, 5:1, 2:1, 1:1; 1:2; 1:5; 1:10; 1:100; 1:200; 1:500; 1:1,000;1:2,000; 1:5,000; 1:10,000; 1:20,000; 1:50,000; 1:100,000; 1:500,000;1:1,000,000; 1:2,000,000; 1:5,000,000; 1:10,000,000; 1:20,000,000;1:50,000,000; or about 1:100,000,000, comparing numbers of totalnucleated cells in each population. Cells in an isolated placental stemcell population can be combined with a plurality of cells of a pluralityof cell types, as well.

In one, an isolated population of placental stem cells is combined witha plurality of hematopoietic stem cells. Such hematopoietic stem cellscan be, for example, contained within unprocessed placental, umbilicalcord blood or peripheral blood; in total nucleated cells from placentalblood, umbilical cord blood or peripheral blood; in an isolatedpopulation of CD34⁺ cells from placental blood, umbilical cord blood orperipheral blood; in unprocessed bone marrow; in total nucleated cellsfrom bone marrow; in an isolated population of CD34⁺ cells from bonemarrow, or the like.

Additional placental stem cells and placental stem cell populations thatcan be used in connection with the compositions and methods providedherein are described, for example, in U.S. patent application Ser. No.11/648,813, and in U.S. Provisional Application No. 60/846,641, each ofwhich is hereby incorporated by reference in its entirety.

5.5.4 Induction of Differentiation Into Hepatic Cells

Differentiation of placental stem cells into hepatic cells can beaccomplished, for example, by placing placental stem cells in cellculture conditions that induce differentiation into hepatic cells. In aspecific embodiment, the placental stem cells are contacted with sodiumbutyrate for a time sufficient for the placental stem cells to exhibitone or more characteristics of a hepatocyte or hepatogenic cell.

An example hepatogenic medium comprises DMEM supplemented with sodiumbutyrate. Cells are cultured, e.g., for 14-28 days, refeeding every 3-4days. Differentiation can be confirmed by assaying for, e.g., increasedproduction of cytokeratin 18 (relative to an undifferentiated placentalstem cell). Typically, placental stem cells express cytokeratin 18, butdo not express at least one other cytokeratin expressed by hepatocytes.Differentiation can also be affirmed by the presence of one or more ofasialogylcoprotein receptor, alpha-1-antitrypsin, albumin and cytochromeP450 activity. A placental stem cell is considered to havedifferentiated into a hepatic cell when the cell displays one or more ofthese characteristics.

In one aspect, provided herein are methods of producing and isolatedpopulation of hepatocytes and/or hepatogenic cells by, e.g., selecting aplurality of placental stem cells, whether derived from enzymaticdigestion or perfusion, that express particular markers and/orparticular culture or morphological characteristics, and exposing suchcells to conditions that cause the differentiation of at least some ofsaid placental stem cells into hepatocytes and/or hepatogenic cells. Inone embodiment, for example, provided herein is a method of producinghepatocytes and/or hepatogenic cells comprising (1) selecting placentalcells that (a) adhere to a substrate, and (b) express CD200 and HLA-G,or express CD73, CD105, and CD200, or express CD200 and OCT-4, orexpress CD73, CD105 and HLA-G, or express CD73 and CD105 and facilitatethe formation of one or more embryoid-like bodies in a population ofplacental cells comprising said stem cell when said population iscultured under conditions that allow for the formation of anembryoid-like body, or express OCT-4 and (c) facilitate the formation ofone or more embryoid-like bodies in a population of placental cellscomprising said stem cell when said population is cultured underconditions that allow for the formation of an embryoid-like body; (2)isolating said placental cells from other placental cells; and exposingsaid cells to sodium butyrate for a time sufficient to produce adetectable number of said hepatocytes and/or hepatogenic cells. In aspecific embodiment, the placental stem cells are CD10⁺, CD34⁻, CD105⁺and CD200⁺.

In various specific embodiments of the above methods, at least, orabout, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, 35%,40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 98% ofsaid placental stem cells differentiate into said hepatocytes and/orhepatogenic cells. In another specific embodiment of any of the aboveembodiments of the method, said placental cells are exposed to sodiumbutyrate for a time sufficient for a plurality of said cells to exhibita detectable increase in the production of cytokeratin 18 relative to anundifferentiated placental stem cell, a detectable amount ofasialogylcoprotein receptor, or a detectable amount of cytochrome P4507A1 activity, a detectable amount of albumin, or a detectable amount ofexpression of a gene encoding albumin. In another specific embodiment,

5.5.5 Induction of Differentiation into Chondrocytic Cells

Chondrogenic differentiation of adherent placental stem cells can beaccomplished, for example, by placing the placental stem cells in cellculture conditions that induce differentiation into chondrocytes. Apreferred chondrocytic medium comprises MSCGM (Cambrex) or Dulbecco'sModified Eagle's Medium (DMEM) supplemented with 15% cord blood serum.In one embodiment, placental stem cells are aliquoted into a sterilepolypropylene tube, centrifuged (e.g., at 150×g for 5 minutes), andwashed twice in Incomplete Chondrogenesis Medium (Cambrex). The cellsare resuspended in Complete Chondrogenesis Medium (Cambrex) containing0.01 μg/ml transforming growth factor beta-3 (TGF-β3) at a concentrationof about 1-20×10⁵ cells/ml. In other embodiments, placental stem cellsare contacted with exogenous growth factors, e.g., GDF-5 or TGF-β3, withor without ascorbate.

Another example chondrogenic medium comprises DMEM, 1% FBS, insulin,ascorbate 2-phosphate, and TGF-β1. A similar chondrogenic mediumcomprises, in 1 L, DMEM, 1% FBS, 1% penicillin-streptomycin, 37.5 μg/mlascorbate-2-phosphate, ITS premix (comprising, e.g., 100 mg of insulin,100 mg of transferrin, and 100 pg of sodium selenate), and 10 ng/mlTGF-1 Another example chondrogenic medium is a defined medium (anystandard defined medium suitable for mammalian cell culture) thatincludes 100 nM dexamethasone and 10 ng/ml transforming growth factor-33(TGF-β3).

Chondrogenic medium can be supplemented with amino acids includingproline and glutamine, sodium pyruvate, dexamethasone, ascorbic acid,and insulin/transferrin/selenium. Chondrogenic medium can besupplemented with sodium hydroxide and/or collagen.

The adherent placental stem cells may be cultured at high or lowdensity. Cells are preferably cultured in the absence of serum.Placental stem cells can be cultured under chondrogenic conditionseither statically or dynamically, e.g., under conditions in which mediumis circulated around cells. Cell culture can proceed for a detectableamount of differentiation occurs. In specific embodiments, adherentplacental stem cells are cultured for about 28 days to about 56 daysunder chondrogenic conditions.

Adherent placental stem cells can be induced to differentiate intochondrocytes or chondrocytic cells by seeding the cells onto anelectrospun nonwoven microfibrous or nanofibrous mat and culturing thecells under chondrogenic conditions. Such mats, and their production,are described in Section 5.7.1.4 herein.

Chondrogenesis can be assessed by e.g., observation of production ofesoinophilic ground substance, safranin-O staining for glycosaminoglycanexpression; methylene blue dye binding for determination ofglycosaminoglycan expression; hematoxylin/eosin staining, assessing cellmorphology, and/or RT/PCR confirmation of, or staining for, collagen 2and collagen 9 gene expression. Chondrogenesis can also be observed bygrowing the stem cells in a pellet, formed, e.g., by gently centrifugingstem cells in suspension (e.g., at about 800 g for about 5 minutes).After about 1-28 days, the pellet of stem cells begins to form a toughmatrix and demonstrates a structural integrity not found in non-induced,or non-chondrogenic, cell lines, pellets of which tend to fall apartwhen challenged. Chondrogenesis can also be demonstrated, e.g., in suchcell pellets, by staining with a stain that stains collagen, e.g.,Sirius Red, and/or a stain that stains glycosaminoglycans (GAGs), suchas, e.g., Alcian Blue (also called Alcian blue 8GX, Ingrain blue 1, orC.I. 74240). A placental stem cell is considered to have differentiatedinto a chondrocytic cell when the cell displays one or more of thesecharacteristics. Chondrogenesis can also be assessed by determination ofgene expression, e.g., by real-time PCR, for early stage chondrogenesismarkers fibromodulin and cartilage oligomeric matrix protein; geneexpression for mid-stage chondrogenesis markers aggrecan, versican,decorin and biglycan; and gene expression for types II and X collagensand chondroadherein, which are markers of mature chondrocytes.

5.6 Preservation of Placental Stem Cells

Placental stem cells, and cells differentiated therefrom, e.g.,hepatocytes and/or hepatogenic cells, chondrocytes and/or chondrocyticcells, can be preserved, that is, placed under conditions that allow forlong-term storage, or conditions that inhibit cell death by, e.g.,apoptosis or necrosis.

Placental stem cells, and cells differentiated therefrom, e.g.,hepatocytes and/or hepatogenic cells, chondrocytes and/or chondrocyticcells, can be preserved using, e.g., a composition comprising anapoptosis inhibitor, necrosis inhibitor and/or an oxygen-carryingperfluorocarbon, as described in related U.S. application Ser. No.11/648,812, entitled “Improved Composition for Collecting Placental StemCells and Preserving Organs” filed on Dec. 28, 2006. In one embodiment,provided herein is a method of preserving a population of cells, e.g.,placental stem cells, and/or hepatocytes and/or hepatogenic cells,chondrocytes and/or chondrocytic cells differentiated therefrom,comprising contacting said cells with a stem cell collection compositioncomprising an inhibitor of apoptosis and an oxygen-carryingperfluorocarbon, wherein said inhibitor of apoptosis is present in anamount and for a time sufficient to reduce or prevent apoptosis in thepopulation of stem cells, as compared to a population of stem cells notcontacted with the inhibitor of apoptosis. In a specific embodiment,said inhibitor of apoptosis is a caspase inhibitor. In another specificembodiment, said inhibitor of apoptosis is a JNK inhibitor. In a morespecific embodiment, said JNK inhibitor does not modulatedifferentiation or proliferation of said cells. In another embodiment,said stem cell collection composition comprises said inhibitor ofapoptosis and said oxygen-carrying perfluorocarbon in separate phases.In another embodiment, said stem cell collection composition comprisessaid inhibitor of apoptosis and said oxygen-carrying perfluorocarbon inan emulsion. In another embodiment, the stem cell collection compositionadditionally comprises an emulsifier, e.g., lecithin. In anotherembodiment, said apoptosis inhibitor and said perfluorocarbon arebetween about 0° C. and about 25° C. at the time of contacting thecells. In another more specific embodiment, said apoptosis inhibitor andsaid perfluorocarbon are between about 2° C. and 10° C., or betweenabout 2° C. and about 5° C., at the time of contacting the cells. Inanother more specific embodiment, said contacting is performed duringtransport of said population of stem cells. In another more specificembodiment, said contacting is performed during freezing and thawing ofsaid population of stem cells.

In another embodiment, provided herein is a method of preserving apopulation of placental stem cells, and/or hepatocytes and/orhepatogenic cells, chondrocytes and/or chondrocytic cells differentiatedtherefrom, comprising contacting said population of cells with aninhibitor of apoptosis and an organ-preserving compound, wherein saidinhibitor of apoptosis is present in an amount and for a time sufficientto reduce or prevent apoptosis in the population of cells, as comparedto a population of cells not contacted with the inhibitor of apoptosis.In a specific embodiment, the organ-preserving compound is UW solution(described in U.S. Pat. No. 4,798,824; also known as VIASPAN®; see alsoSouthard et al., Transplantation 49(2):251-257 (1990)) or a solutiondescribed in Stern et al., U.S. Pat. No. 5,552,267. In anotherembodiment, said organ-preserving compound is hydroxyethyl starch,lactobionic acid, raffinose, or a combination thereof. In anotherembodiment, the stem cell collection composition additionally comprisesan oxygen-carrying perfluorocarbon, either in two phases or as anemulsion.

In another embodiment of the method, placental stem cells are contactedwith a stem cell collection composition comprising an apoptosisinhibitor and oxygen-carrying perfluorocarbon, organ-preservingcompound, or combination thereof, during perfusion. In anotherembodiment, said cells are contacted during a process of tissuedisruption, e.g., enzymatic digestion. In another embodiment, placentalstem cells are contacted with said stem cell collection compound aftercollection by perfusion, or after collection by tissue disruption, e.g.,enzymatic digestion.

Typically, during placental cell collection, enrichment and isolation,it is preferable to minimize or eliminate cell stress due to hypoxia andmechanical stress. In another embodiment of the method, therefore, astem cell, or population of stem cells, is exposed to a hypoxiccondition during collection, enrichment or isolation for less than sixhours during said preservation, wherein a hypoxic condition is aconcentration of oxygen that is less than normal blood oxygenconcentration. In a more specific embodiment, said population of stemcells is exposed to said hypoxic condition for less than two hoursduring said preservation. In another more specific embodiment, saidpopulation of stem cells is exposed to said hypoxic condition for lessthan one hour, or less than thirty minutes, or is not exposed to ahypoxic condition, during collection, enrichment or isolation. Inanother specific embodiment, said population of stem cells is notexposed to shear stress during collection, enrichment or isolation.

The placental stem cells used in the compositions and methods providedherein can be cryopreserved, e.g., in cryopreservation medium in smallcontainers, e.g., ampoules. Suitable cryoprescrvation medium includes,but is not limited to, culture medium including, e.g., growth medium, orcell freezing medium, for example commercially available cell freezingmedium, e.g., C2695, C2639 or C6039 (Sigma). Cryopreservation mediumpreferably comprises DMSO (dimethylsulfoxide), at a concentration of,e.g., about 10% (v/v). Cryopreservation medium may comprise additionalagents, for example, methylcellulose and/or glycerol. Placental stemcells are preferably cooled at about 1° C./min during cryopreservation.A preferred cryopreservation temperature is about −80° C. to about −180°C., preferably about −125° C. to about −140° C. Cryopreserved cells canbe transferred to liquid nitrogen prior to thawing for use. In someembodiments, for example, once the ampoules have reached about −90° C.,they are transferred to a liquid nitrogen storage area. Cryopreservedcells preferably are thawed at a temperature of about 25° C. to about40° C., preferably to a temperature of about 37° C.

5.7 Uses of Placental Stem Cells

5.7.1 Compositions Comprising Placental Stem Cells

The methods described herein can use compositions comprising placentalstem cells, or biomolecules therefrom. In the same manner, thepluralities and populations of placental stem cells described herein canbe combined with any physiologically-acceptable or medically-acceptablecompound, composition or device for use in, e.g., research ortherapeutics.

5.7.1.1 Cryopreserved Placental Stem Cells

The placental stem cell populations described herein can be preserved,for example, cryopreserved for later use. Methods for cryopreservationof cells, such as stem cells, are well known in the art. Placental stemcell populations can be prepared in a form that is easily administrableto an individual. For example, provided herein is a placental stem cellpopulation that is contained within a container that is suitable formedical use. Such a container can be, for example, a sterile plasticbag, flask, jar, or other container from which the placental stem cellpopulation can be easily dispensed. For example, the container can be ablood bag or other plastic, medically-acceptable bag suitable for theintravenous administration of a liquid to a recipient. The container ispreferably one that allows for cryopreservation of the combined stemcell population.

Cryopreserved placental stem cell populations can comprise placentalstem cells derived from a single donor, or from multiple donors. Theplacental stem cell population can be completely HLA-matched to anintended recipient, or partially or completely HLA-mismatched.

Cryopreserved placental stem cells can be, for example, in the form of acomposition comprising an placental stem cell population in a container.In a specific embodiment, the stem cell population is cryopreserved. Inanother specific embodiment, the container is a bag, flask, or jar. In amore specific embodiment, said bag is a sterile plastic bag. In a morespecific embodiment, said bag is suitable for, allows or facilitatesintravenous administration of said placental stem cell population. Thebag can comprise multiple lumens or compartments that are interconnectedto allow mixing of the placental stem cells and one or more othersolutions, e.g., a drug, prior to, or during, administration. In anotherspecific embodiment, the composition comprises one or more compoundsthat facilitate cryopreservation of the combined stem cell population.In another specific embodiment, said placental stem cell population iscontained within a physiologically-acceptable aqueous solution. In amore specific embodiment, said physiologically-acceptable aqueoussolution is a 0.9% NaCl solution. In another specific embodiment, saidplacental stem cell population comprises placental cells that areHLA-matched to a recipient of said stem cell population. In anotherspecific embodiment, said combined stem cell population comprisesplacental cells that are at least partially HLA-mismatched to arecipient of said stem cell population. In another specific embodiment,said placental stem cells are derived from a plurality of donors.

5.7.1.2 Pharmaceutical Compositions

Populations of placental stem cells, or populations of cells comprisingplacental stem cells, can be formulated into pharmaceutical compositionsfor use in vivo. Such pharmaceutical compositions comprise a populationof placental stem cells, or a population of cells comprising placentalstem cells, in a pharmaceutically-acceptable carrier, e.g., a salinesolution or other accepted physiologically-acceptable solution for invivo administration. Pharmaceutical compositions provided herein,comprising placental stem cells, can comprise any of the placental stemcell populations, or placental stem cell types, described elsewhereherein. The pharmaceutical compositions can comprise fetal, maternal, orboth fetal and maternal placental stem cells. The pharmaceuticalcompositions can further comprise placental stem cells obtained from asingle individual or placenta, or from a plurality of individuals orplacentae.

The pharmaceutical compositions can comprise any number of placentalstem cells. For example, a single unit dose of placental stem cells cancomprise, in various embodiments, about, at least, or no more than1×10⁵, 5×10⁵, 1×10⁶, 5×10⁶, 1×10⁷, 5×10⁷, 1×10⁸, 5×10⁸, 1×10⁹, 5×10⁹,1×10¹⁰, 5×10¹⁰, 1×10¹¹ or more placental stem cells.

The pharmaceutical compositions may comprise populations of cells thatcomprise 50% viable cells or more (that is, at least 50% of the cells inthe population are functional or living). Preferably, at least 60% ofthe cells in the population are viable. More preferably, at least 70%,80%, 90%, 95%, or 99% of the cells in the population in thepharmaceutical composition are viable.

The pharmaceutical compositions provided herein can comprise one or morecompounds that, e.g., facilitate engraftment (e.g., anti-T-cell receptorantibodies, an immunosuppressant, or the like); stabilizers such asalbumin, dextran 40, gelatin, hydroxyethyl starch, and the like.

5.7.1.3 Placental Stem Cell Conditioned Media

The placental stem cells provided herein can be used to produceconditioned medium, that is, medium comprising one or more biomoleculessecreted or excreted by the stem cells. In various embodiments, theconditioned medium comprises medium in which placental stem cells havegrown for at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or moredays. In other embodiments, the conditioned medium comprises medium inwhich placental stem cells have grown to at least 30%, 40%, 50%, 60%,70%, 80%, 90% confluence, or up to 100% confluence. Such conditionedmedium can be used to support the culture of a separate population ofplacental stem cells, or stem cells of another kind. In anotherembodiment, the conditioned medium comprises medium in which placentalstem cells have been differentiated into an adult cell type. In anotherembodiment, conditioned medium comprises medium in which placental stemcells and non-placental stem cells have been cultured.

Thus, in one embodiment, provided herein is a composition comprisingculture medium, e.g., conditioned medium, from a culture of adherentplacental stem cells, wherein said adherent placental stem cells (a)adhere to a substrate; (b) express CD200 and HLA-G, or express CD73,CD105, and CD200, or express CD200 and OCT-4, or express CD73, CD105,and HLA-G, or express CD73 and CD105 and facilitate the formation of oneor more embryoid-like bodies in a population of placental cells thatcomprise the placental stem cells, when said population is culturedunder conditions that allow formation of embryoid-like bodies, orexpress OCT-4 and facilitate the formation of one or more embryoid-likebodies in a population of placental cells that comprise the placentalstem cells when said population is cultured under conditions that allowformation of embryoid-like bodies, wherein said culture of placentalstem cells has been cultured in said medium for 24 hours or more. In aspecific embodiment, said composition comprises medium conditioned byCD34⁺, CD45⁻ placental stem cells. In another specific embodiment, thecomposition further comprises a plurality of said placental stem cells,e.g., a plurality of adherent placental stem cells and/or a plurality ofnon-adherent, CD34⁺, CD45⁻ placental stem cells. In another specificembodiment, the composition comprises a plurality of non-placentalcells. In a more specific embodiment, said non-placental cells compriseCD34⁺ cells, e.g., hematopoietic progenitor cells, derived from anon-placental source such as peripheral blood hematopoietic progenitorcells, cord blood hematopoietic progenitor cells, or placental bloodhematopoietic progenitor cells. The non-placental cells can alsocomprise other stem cells, such as mesenchymal stem cells, e.g., bonemarrow-derived mesenchymal stem cells. The non-placental cells can alsobe one ore more types of adult cells or cell lines. In another specificembodiment, the composition comprises an anti-proliferative agent, e.g.,an anti-MIP-1α or anti-MIP-1β antibody.

In another embodiment, conditioned medium is, or comprises, mediumconditioned by a population of hepatocytes, hepatogenic cells,chondrocytes and/or chondrocytic cells differentiated from placentalstem cells. Such a population can comprise placental stem cells,hepatogenic cells or chondrogenic cells differentiated from placentalstem cells, hepatocytes or chondrocytes differentiated from placentalstem cells, or any combination of the foregoing. Thus, in oneembodiment, provided herein is a composition comprising culture mediumfrom a culture of hepatocytes, hepatogenic cells, chondrocytes and/orchondrocytic cells differentiated from placental stem cells, whereinsaid placental stem cells (a) adhere to a substrate; (b) express CD200and HLA-G, or express CD73, CD105, and CD200, or express CD200 andOCT-4, or express CD73, CD105, and HLA-G, or express CD73 and CD105 andfacilitate the formation of one or more embryoid-like bodies in apopulation of placental cells that comprise the placental stem cells,when said population is cultured under conditions that allow formationof embryoid-like bodies, or express OCT-4 and facilitate the formationof one or more embryoid-like bodies in a population of placental cellsthat comprise the placental stem cells when said population is culturedunder conditions that allow formation of embryoid-like bodies, whereinsaid culture of hepatocytes, hepatogenic cells, chondrocytes and/orchondrocytic cells has been cultured in said medium for 24 hours ormore. In a specific embodiment, the composition further comprises aplurality of said placental stem cells. In another specific embodiment,the composition comprises a plurality of non-placental cells, e.g.,hepatocytes from primary culture; hepatocyte cell line cells; hepatomacells, and the like. In a more specific embodiment, said non-placentalcells comprise CD34⁺ cells, e.g., hematopoietic progenitor cells, suchas peripheral blood hematopoietic progenitor cells, cord bloodhematopoietic progenitor cells, or placental blood hematopoieticprogenitor cells. The non-placental cells can also comprise other stemcells, such as mesenchymal stem cells, e.g., bone marrow-derivedmesenchymal stem cells. The non-placental cells can also be one ore moretypes of adult cells or cell lines. In another specific embodiment, thecomposition comprises an anti-proliferative agent, e.g., an anti-MIP-1αor anti-MIP-1β antibody.

5.7.1.4 Matrices Comprising Placental Stem Cells

In another aspect, provided herein are matrices, hydrogels, scaffolds,and the like that comprise a population of hepatocytes, hepatogeniccells, chondrocytes and/or chondrocytic cells, differentiated from theadherent placental stem cells described herein.

Placental stem cells, or hepatocytes, hepatogenic cells, chondrocytesand/or chondrocytic cells differentiated from the placental stem cells,can be seeded onto a natural matrix, e.g., a placental biomaterial suchas an amniotic membrane material. Such an amniotic membrane material canbe, e.g., amniotic membrane dissected directly from a mammalianplacenta; fixed or heat-treated amniotic membrane, substantially dry(i.e., <20% H₂O) amniotic membrane, chorionic membrane, substantiallydry chorionic membrane, substantially dry amniotic and chorionicmembrane, and the like. Preferred placental biomaterials on whichplacental stem cells can be seeded are described in Hariri, U.S.Application Publication No. 2004/0048796.

Placental stem cells, or cells differentiated therefrom, e.g.,hepatocytes, hepatogenic cells, chondrocytes and/or chondrocytic cells,can be suspended in a hydrogel solution suitable for, e.g., injection.Suitable hydrogels for such compositions include self-assemblingpeptides, such as RAD16. In one embodiment, a hydrogel solutioncomprising the cells can be allowed to harden, for instance in a mold,to form a matrix having cells dispersed therein for implantation. Cellsin such a matrix can also be cultured so that the cells are mitoticallyexpanded prior to implantation. The hydrogel can be, e.g., an organicpolymer (natural or synthetic) that is cross-linked via covalent, ionic,or hydrogen bonds to create a three-dimensional open-lattice structurethat entraps water molecules to form a gel. Hydrogel-forming materialsinclude polysaccharides such as alginate and salts thereof, peptides,polyphosphazines, and polyacrylates, which are crosslinked ionically, orblock polymers such as polyethylene oxide-polypropylene glycol blockcopolymers which are crosslinked by temperature or pH, respectively. Insome embodiments, the hydrogel or matrix is biodegradable.

In some embodiments, the formulation comprises an in situ polymerizablegel (see, e.g., U.S. Patent Application Publication 2002/0022676; Ansethet al., J. Control Release, 78(1-3): 199-209 (2002); Wang et al.,Biomaterials, 24(22):3969-80 (2003).

In some embodiments, the polymers are at least partially soluble inaqueous solutions, such as water, buffered salt solutions, or aqueousalcohol solutions, that have charged side groups, or a monovalent ionicsalt thereof. Examples of polymers having acidic side groups that can bereacted with cations are poly(phosphazenes), poly(acrylic acids),poly(methacrylic acids), copolymers of acrylic acid and methacrylicacid, poly(vinyl acetate), and sulfonated polymers, such as sulfonatedpolystyrene. Copolymers having acidic side groups formed by reaction ofacrylic or methacrylic acid and vinyl ether monomers or polymers canalso be used. Examples of acidic groups are carboxylic acid groups,sulfonic acid groups, halogenated (preferably fluorinated) alcoholgroups, phenolic OH groups, and acidic OH groups.

The placental stem cells, or hepatocytes, hepatogenic cells,chondrocytes and/or chondrocytic cells differentiated from the placentalstem cells, or co-cultures thereof can be seeded onto athree-dimensional framework or scaffold and implanted in vivo. Such aframework can be implanted in combination with any one or more growthfactors, cells, drugs or other components that stimulate tissueformation.

Examples of scaffolds that can be used include nonwoven mats, porousfoams, or self assembling peptides. Nonwoven mats can be formed usingfibers comprised of a synthetic absorbable copolymer of glycolic andlactic acids (e.g., PGA/PLA) (VICRYL, Ethicon, Inc., Somerville, N.J.).Foams, composed of, e.g., poly(s-caprolactone)/poly(glycolic acid)(PCL/PGA) copolymer, formed by processes such as freeze-drying, orlyophilization (see, e.g., U.S. Pat. No. 6,355,699), can also be used asscaffolds.

In another embodiment, the scaffold is, or comprises, a nanofibrousscaffold, e.g., an electrospun nanofibrous scaffold. In a more specificembodiment, said nanofibrous scaffold comprises poly(L-lactic acid)(PLLA), poly lactic glycolic acid (PLGA), type I collagen, a copolymerof vinylidene fluoride and trifluoroethylnee (PVDF-TrFE),poly(-caprolactone), poly(L-lactide-co-ε-caprolactone) [P(LLA-CL)](e.g., 75:25), and/or a copolymer ofpoly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and type I collagen.In another more specific embodiment, said scaffold promotes thedifferentiation of placental stem cells into chondrocytes. Methods ofproducing nanofibrous scaffolds, e.g., electrospun nanofibrousscaffolds, are known in the art. See, e.g., Xu et al., TissueEngineering 10(7): 1160-1168 (2004); Xu et al., Biomaterials 25:877-886(20040; Meng et al., J. Biomaterials Sci., Polymer Edition 18(1):81-94(2007).

The compositions listed above can be electrospun into a nonwoven matcomprising nanoscale fiber meshes with controllable porosity. Inelectrospinning, a high voltage is used to create an electricallycharged jet of polymer solution, which dries or solidifies to leave apolymer fiber. One electrode is placed into the polymer solution in,e.g., a tube or capillary, e.g., a needle, and the other attached to acollector. An electric field is passed to the end of the tube orcapillary, inducing a charge on the surface of the liquid. Mutual chargerepulsion causes a force directly opposite to the surface tension of thesolution. As the intensity of the electric field is increased, therepulsive electrostatic force overcomes the surface tension, and acharged jet of fluid is ejected from the solution at the tip of the tubeor capillary. Solvent in the discharged polymer solution jet evaporates,leaving behind a charged polymer fiber, which lays itself randomly on agrounded collecting metal screen. The thickness of the mat, and thethickness of the fibers in the mat, can be adjusted by increasing ordecreasing the distance between tube and collection screen, withincreasing distance generally resulting in finer fibers and a less-densemat; by increasing or decreasing the electric potential, in kilovolts,with increasing potential generally resulting in decreased fiberthickness; by increasing or decreasing the flow rate, with increasingflow rate generally resulting in thicker fibers; or increasing ordecreasing the polymer concentration in solution, with increasingpolymer concentration generally resulting in increased fiber thickness.The diameter of the tube at the tip can also be varied. In specificembodiments, any polymer, e.g., any of the polymers disclosed herein,suitable for electrospinning to create nanoscale nonwoven fibrous meshesor mats, e.g., PLLA or PLGA, can be electrospun at a voltage of, e.g.,about 5 kV, 10 kV, 15 kV, 20 kV, 25 kV, 30 kV, 35 kV or about 40 kV; andthe needle distance can be varied, e.g., from about 1, 2, 3, 4, 5, 6, 7,8, 9, 0, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42,44, 46, 48 or about 50 cm between needle tip and collection screen. Theneedle gauge can be varied, e.g., from about 8 G to about 24 G, e.g., 12G or 22 G. The flow rate can be varied, e.g., from about 0.01 to about1.0 mL/min, e.g., about 0.05 to about 0.1 mL/min. The solutionconcentration, using any of the polymers, can range from about 5% toabout 50% w/w in solution, e.g., about 10% to about 25% w/w. In specificembodiments, PLLA or PLGA at about 10% to about 25% w/w in solution canbe electrospun using a 12 G needle or 22 G needle using a tip tocollection screen distance of 30 cm and a flow rate of about 0.05 mL/minto about 0.1 mL/min to produce electrospun mats comprising fibers of anaverage diameter of about 250 nm to about 10 μm.

Placental stem cells of the invention can also be seeded onto, orcontacted with, a physiologically-acceptable ceramic material including,but not limited to, mono-, di-, tri-, alpha-tri-, beta-tri-, andtetra-calcium phosphate, hydroxyapatite, fluoroapatites, calciumsulfates, calcium fluorides, calcium oxides, calcium carbonates,magnesium calcium phosphates, biologically active glasses such asBIOGLASS®, and mixtures thereof. Porous biocompatible ceramic materialscurrently commercially available include SURGIBONE® (CanMedica Corp.,Canada), ENDOBON® (Merck Biomaterial France, France), CEROS® (Mathys,AG, Bettlach, Switzerland), and mineralized collagen bone graftingproducts such as HEALOS™ (DePuy, Inc., Raynham, Mass.) and VITOSS®,RHAKOSS™, and CORTOSS® (Orthovita, Malvern, Pa.). The framework can be amixture, blend or composite of natural and/or synthetic materials.

In another embodiment, placental stem cells, or hepatocytes and/orhepatogenic cells differentiated from the placental stem cells, can beseeded onto, or contacted with, a felt, which can be, e.g., composed ofa multifilament yarn made from a bioabsorbable material such as PGA,PLA, PCL copolymers or blends, or hyaluronic acid.

The placental stem cells, or hepatocytes, hepatogenic cells,chondrocytes and/or chondrocytic cells differentiated from the placentalstem cells, can, in another embodiment, be seeded onto foam scaffoldsthat may be composite structures. Such foam scaffolds can be molded intoa useful shape, such as that of a portion of a specific structure in thebody to be repaired, replaced or augmented. In some embodiments, theframework is treated, e.g., with 0.1M acetic acid followed by incubationin polylysine, PBS, and/or collagen, prior to inoculation of cells inorder to enhance cell attachment. External surfaces of a matrix may bemodified to improve the attachment or growth of cells anddifferentiation of tissue, such as by plasma-coating the matrix, oraddition of one or more proteins (e.g., collagens, elastic fibers,reticular fibers), glycoproteins, glycosaminoglycans (e.g., heparinsulfate, chondroitin-4-sulfate, chondroitin-6-sulfate, dermatan sulfate,keratin sulfate, etc.), a cellular matrix, and/or other materials suchas, but not limited to, gelatin, alginates, agar, agarose, and plantgums, and the like.

In some embodiments, the scaffold comprises, or is treated with,materials that render it non-thrombogenic. These treatments andmaterials may also promote and sustain endothelial growth, migration,and extracellular matrix deposition. Examples of these materials andtreatments include but are not limited to natural materials such asbasement membrane proteins such as laminin and Type IV collagen,synthetic materials such as EPTFE, and segmented polyurethaneureasilicones, such as PURSPAN™ (The Polymer Technology Group, Inc.,Berkeley, Calif.). The scaffold can also comprise anti-thrombotic agentssuch as heparin; the scaffolds can also be treated to alter the surfacecharge (e.g., coating with plasma) prior to seeding with placental stemcells.

Thus, in another aspect, provided herein is a composition comprisingisolated adherent CD10⁺, CD34⁻, CD105⁺, CD200⁺ placental stem cells andan electrospun nanofibrous scaffold. In a specific embodiment, saidnanofibrous scaffold comprises fibers of poly(L-lactic acid) (PLLA),poly lactic glycolic acid (PLGA), type I collagen, a copolymer ofvinylidene fluoride and trifluoroethylnee (PVDF-TrFE),poly(-caprolactone), poly(L-lactide-co-ε-caprolactone) [P(LLA-CL)](e.g., 75:25), and/or a copolymer ofpoly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and type I collagen.In another specific embodiment, said nanofibrous scaffold comprisesfibers that average between about 250 nanometers and about 10 m inthickness. In another specific embodiment, said composition is contactedwith conditions in which the placental stem cells differentiate intochondrogenic cells or chondrocytes. In another embodiment, providedherein is a method of making a composition comprising contactingadherent CD10⁺, CD34⁻, CD105⁺, CD200⁺ placental stem cells with anelectrospun nanofibrous scaffold, wherein said nanofibrous scaffold ismade by electrospinning PLLA or PLGA at about 20 kV at about 30 cmneedle to collector distance and about 0.05 mL/min. to about 0.1 mL/minflow rate, wherein said PLLA or PLGA are in solution at about 10% w/w toabout 20% w/w.

5.7.2 Genetically Modified Placental Stem Cells

In another aspect, the placental stem cells and umbilical cord stemcells described herein can be genetically modified, e.g., to produce anucleic acid or polypeptide of interest, or to produce a differentiatedcell, e.g., a hepatocyte, hepatogenic cell, chondrocyte and/orchondrocytic cell, that produces a nucleic acid or polypeptide ofinterest. Genetic modification can be accomplished, e.g., usingvirus-based vectors including, but not limited to, non-integratingreplicating vectors, e.g., papilloma virus vectors, SV40 vectors,adenoviral vectors; integrating viral vectors, e.g., retrovirus vectoror adeno-associated viral vectors; or replication-defective viralvectors. Other methods of introducing DNA into cells include the use ofliposomes, electroporation, a particle gun, direct DNA injection, or thelike.

Stem cells can be, e.g., transformed or transfected with DNA controlledby or in operative association with, one or more appropriate expressioncontrol elements, for example, promoter or enhancer sequences,transcription terminators, polyadenylation sites, internal ribosomalentry sites. Preferably, such a DNA incorporates a selectable marker.Following the introduction of the foreign DNA, engineered stem cells canbe, e.g., grown in enriched media and then switched to selective media.In one embodiment, the DNA used to engineer a placental stem cellcomprises a nucleotide sequence encoding a polypeptide of interest,e.g., a cytokine, growth factor, differentiation agent, or therapeuticpolypeptide.

The DNA used to engineer the stem cell can comprise any promoter knownin the art to drive expression of a nucleotide sequence in mammaliancells, e.g., human cells. For example, promoters include, but are notlimited to, CMV promoter/enhancer, SV40 promoter, papillomaviruspromoter, Epstein-Barr virus promoter, elastin gene promoter, and thelike. In a specific embodiment, the promoter is regulatable so that thenucleotide sequence is expressed only when desired. Promoters can beeither inducible (e.g., those associated with metallothionein and heatshock proteins) or constitutive.

In another specific embodiment, the promoter is tissue-specific orexhibits tissue specificity. Examples of such promoters include but arenot limited to: myelin basic protein gene control region (Readhead etal., 1987, Cell 48:703) (oligodendrocyte cells); elastase I gene controlregion (Swit et al., 1984, Cell 38:639; Ornitz et al., 1986, Cold SpringHarbor Symp. Quant. Biol. 50:399; MacDonald, 1987, Hepatology 7:425)(pancreatic acinar cells); insulin gene control region (Hanahan, 1985,Nature 315:115) (pancreatic beta cells); myosin light chain-2 genecontrol region (Shani, 1985, Nature 314:283) (skeletal muscle).

The cells of the invention may be engineered to “knock out” or “knockdown” expression of one or more genes. The expression of a gene nativeto a cell can be diminished by, for example, inhibition of expression byinactivating the gene completely by, e.g., homologous recombination. Inone embodiment, for example, an exon encoding an important region of theprotein, or an exon 5′ to that region, is interrupted by a positiveselectable marker, e.g., neo, preventing the production of normal mRNAfrom the target gene and resulting in inactivation of the gene. A genemay also be inactivated by creating a deletion in part of a gene or bydeleting the entire gene. By using a construct with two regions ofhomology to the target gene that are far apart in the genome, thesequences intervening the two regions can be deleted (Mombaerts et al.,1991, Proc. Nat. Acad. Sci. U.S.A. 88:3084). Antisense, DNAzymes, smallinterfering RNA, and ribozyme molecules that inhibit expression of thetarget gene can also be used to reduce the level of target gene activityin the stem cells. For example, antisense RNA molecules which inhibitthe expression of major histocompatibility gene complexes (HLA) havebeen shown to be most versatile with respect to immune responses. Triplehelix molecules can be utilized in reducing the level of target geneactivity. See, e.g., L. G. Davis et al. (eds), 1994, BASIC METHODS INMOLECULAR BIOLOGY, 2nd ed., Appleton & Lange, Norwalk, Conn., which isincorporated herein by reference.

In a specific embodiment, the placental or umbilical cord stem cells ofthe invention can be genetically modified with a nucleic acid moleculecomprising a nucleotide sequence encoding a polypeptide of interest,wherein expression of the polypeptide of interest is controllable by anexogenous factor, e.g., polypeptide, small organic molecule, or thelike. Such a polypeptide can be a therapeutic polypeptide. In a morespecific embodiment, the polypeptide of interest is IL-12 orinterleukin-1 receptor antagonist (IL-1Ra). In another more specificembodiment, the polypeptide of interest is a fusion of interleukin-1receptor antagonist and dihydrofolate reductase (DHFR), and theexogenous factor is an antifolate, e.g., methotrexate. Such a constructis useful in the engineering of placental or umbilical cord stem cellsthat express IL-1Ra, or a fusion of IL-1Ra and DHFR, upon contact withmethotrexate. Such a construct can be used, e.g., in the treatment ofrheumatoid arthritis. In this embodiment, the fusion of IL-1Ra and DHFRis translationally upregulated upon exposure to an antifolate such asmethotrexate. Therefore, in another specific embodiment, the nucleicacid used to genetically engineer a placental stem cell or umbilicalcord stem cell can comprise nucleotide sequences encoding a firstpolypeptide and a second polypeptide, wherein said first and secondpolypeptides are expressed as a fusion protein that is translationallyupregulated in the presence of an exogenous factor. The polypeptide canbe expressed transiently or long-term (e.g., over the course of weeks ormonths).

Such a nucleic acid molecule can additionally comprise a nucleotidesequence encoding a polypeptide that allows for positive selection ofengineered stem cells, or allows for visualization of the engineeredstem cells. In another more specific embodiment, the nucleotide sequenceencodes a polypeptide that is, e.g., fluorescent under appropriatevisualization conditions, e.g., luciferase (Luc). In a more specificembodiment, such a nucleic acid molecule can compriseIL-1Ra-DHFR-IRES-Luc, where IL-1Ra is interleukin-1 receptor antagonist,IRES is an internal ribosomal entry site, and DHFR is dihydrofolatereductase.

5.7.3 Immortalized Placental Stem Cell Lines

Mammalian placental cells can be conditionally immortalized bytransfection with any suitable vector containing a growth-promotinggene, that is, a gene encoding a protein that, under appropriateconditions, promotes growth of the transfected cell, such that theproduction and/or activity of the growth-promoting protein isregulatable by an external factor. In a preferred embodiment thegrowth-promoting gene is an oncogene such as, but not limited to, v-myc,N-myc, c-myc, p53, SV40 large T antigen, polyoma large T antigen, E1aadenovirus or E7 protein of human papillomavirus.

External regulation of the growth-promoting protein can be achieved byplacing the growth-promoting gene under the control of anexternally-regulatable promoter, e.g., a promoter the activity of whichcan be controlled by, for example, modifying the temperature of thetransfected cells or the composition of the medium in contact with thecells. in one embodiment, a tetracycline (tet)-controlled geneexpression system can be employed (see Gossen et al., Proc. Natl. Acad.Sci. USA 89:5547-5551, 1992; Hoshimaru et al., Proc. Nall. Acad. Sci.USA 93:1518-1523, 1996). In the absence of tet, a tet-controlledtransactivator (tTA) within this vector strongly activates transcriptionfrom ph_(CMV*-1), a minimal promoter from human cytomegalovirus fused totet operator sequences. tTA is a fusion protein of the repressor (tetR)of the transposon-10-derived tet resistance operon of Escherichia coliand the acidic domain of VP 16 of herpes simplex virus. Low, non-toxicconcentrations of tet (e.g., 0.01-1.0 μg/mL) almost completely abolishtransactivation by tTA.

In one embodiment, the vector further contains a gene encoding aselectable marker, e.g., a protein that confers drug resistance. Thebacterial neomycin resistance gene (neo^(R)) is one such marker that maybe employed. Cells carrying neo^(R) may be selected by means known tothose of ordinary skill in the art, such as the addition of, e.g.,100-200 μg/mL G418 to the growth medium.

Transfection can be achieved by any of a variety of means known to thoseof ordinary skill in the art including, but not limited to, retroviralinfection. In general, a cell culture may be transfected by incubationwith a mixture of conditioned medium collected from the producer cellline for the vector and DMEM/FI2 containing N2 supplements. For example,a placental cell culture prepared as described above may be infectedafter, e.g., five days in vitro by incubation for about 20 hours in onevolume of conditioned medium and two volumes of DMEM/F12 containing N2supplements. Transfected cells carrying a selectable marker may then beselected as described above.

Following transfection, cultures are passaged onto a surface thatpermits proliferation, e.g., allows at least 30% of the cells to doublein a 24 hour period. Preferably, the substrate is apolyornithine/laminin substrate, consisting of tissue culture plasticcoated with polyornithine (10 μg/mL) and/or laminin (10 μg/mL), apolylysine/laminin substrate or a surface treated with fibronectin.Cultures are then fed every 3-4 days with growth medium, which may ormay not be supplemented with one or more proliferation-enhancingfactors. Proliferation-enhancing factors may be added to the growthmedium when cultures are less than 50% confluent.

The conditionally-immortalized placental stem cell lines can be passagedusing standard techniques, such as by trypsinization, when 80-95%confluent. Up to approximately the twentieth passage, it is, in someembodiments, beneficial to maintain selection (by, for example, theaddition of G418 for cells containing a neomycin resistance gene). Cellsmay also be frozen in liquid nitrogen for long-term storage.

Clonal cell lines can be isolated from a conditionally-immortalizedhuman placental stem cell line prepared as described above. In general,such clonal cell lines may be isolated using standard techniques, suchas by limit dilution or using cloning rings, and expanded. Clonal celllines may generally be fed and passaged as described above.

Conditionally-immortalized human placental stem cell lines, which may,but need not, be clonal, may generally be induced to differentiate bysuppressing the production and/or activity of the growth-promotingprotein under culture conditions that facilitate differentiation. Forexample, if the gene encoding the growth-promoting protein is under thecontrol of an externally-regulatable promoter, the conditions, e.g.,temperature or composition of medium, may be modified to suppresstranscription of the growth-promoting gene. For thetetracycline-controlled gene expression system discussed above,differentiation can be achieved by the addition of tetracycline tosuppress transcription of the growth-promoting gene. In general, 1 μg/mLtetracycline for 4-5 days is sufficient to initiate differentiation. Topromote further differentiation, additional agents may be included inthe growth medium.

5.7.4 Assays

The placental stem cells, or hepatocytes and/or hepatogenic cells,described herein can be used in assays to determine the influence ofculture conditions, environmental factors, molecules (e.g.,biomolecules, small inorganic molecules. etc.) and the like on theproliferation, expansion, and/or differentiation of such cells, comparedto cells not exposed to such conditions.

In one embodiment, the hepatocytes and/or hepatogenic cells describedherein are assayed for changes in proliferation, expansion ordifferentiation upon contact with a molecule. In one embodiment, forexample, provided herein is a method of identifying a compound thatmodulates the proliferation of a plurality of hepatocytes and/orhepatogenic cells differentiated from placental stem cells, comprisingcontacting said cells with said compound under conditions that allowproliferation, wherein if said compound causes a detectable change inproliferation of said cells compared to such cells not contacted withsaid compound, said compound is identified as a compound that modulatesproliferation of hepatocytes and/or hepatogenic cells. In a specificembodiment, said compound is identified as an inhibitor ofproliferation. In another specific embodiment, said compound isidentified as an enhancer of proliferation.

In another embodiment, provided herein is a method of identifying acompound that modulates the expansion of a plurality of hepatocytesand/or hepatogenic cells differentiated from placental stem cells,comprising contacting said hepatocytes and/or hepatogenic cells withsaid compound under conditions that allow expansion, wherein if saidcompound causes a detectable change in expansion of said hepatocytesand/or hepatogenic cells compared to a plurality of hepatocytes and/orhepatogenic cells not contacted with said compound, said compound isidentified as a compound that modulates expansion of hepatocytes and/orhepatogenic cells. In a specific embodiment, said compound is identifiedas an inhibitor of expansion. In another specific embodiment, saidcompound is identified as an enhancer of expansion.

In another embodiment, provided herein is a method of identifying acompound that modulates the differentiation of a placental stem cell,e.g., differentiation to a hepatocyte and/or a hepatogenic cell,comprising contacting said stem cells with said compound underconditions that allow differentiation to a hepatocyte or a hepatogeniccell, wherein if said compound causes a detectable change indifferentiation of said stem cells compared to a stem cell not contactedwith said compound, said compound is identified as a compound thatmodulates proliferation of placental stem cells. In a specificembodiment, said compound is identified as an inhibitor ofdifferentiation. In another specific embodiment, said compound isidentified as an enhancer of differentiation.

5.7.5 Cell Banks

Stem cells from postpartum placentas can be cultured in a number ofdifferent ways to produce a set of lots, e.g., a set ofindividually-administrable doses, of placental stem cells. Such lotscan, for example, be obtained from stem cells from placental perfusateor from enzyme-digested placental tissue. Sets of lots of placental stemcells, obtained from a plurality of placentas, can be arranged in a bankof placental stem cells for, e.g., long-term storage. Generally,adherent stem cells are obtained from an initial culture of placentalmaterial to form a seed culture, which is expanded under controlledconditions to form populations of cells from approximately equivalentnumbers of doublings. Lots are preferably derived from the tissue of asingle placenta, but can be derived from the tissue of a plurality ofplacentas.

In one embodiment, stem cell lots are obtained as follows. Placentaltissue is first disrupted, e.g., by mincing, digested with a suitableenzyme, e.g., collagenase (see Section 5.2.3, above). The placentaltissue preferably comprises, e.g., the entire amnion, entire chorion, orboth, from a single placenta, but can comprise only a part of either theamnion or chorion. The digested tissue is cultured, e.g., for about 1-3weeks, preferably about 2 weeks. After removal of non-adherent cells,high-density colonies that form are collected, e.g., by trypsinization.These cells are collected and resuspended in a convenient volume ofculture medium, and defined as Passage 0 cells.

Passage 0 cells are then used to seed expansion cultures. Expansioncultures can be any arrangement of separate cell culture apparatuses,e.g., a Cell Factory by NUNC™. Cells in the Passage 0 culture can besubdivided to any degree so as to seed expansion cultures with, e.g.,1×10³, 2×10³, 3×10³, 4×10³, 5×10³, 6×10³, 7×10³, 8×10³, 9×10³, 1×10⁴,1×10⁴, 2×10⁴, 3×10⁴, 4×10⁴, 5×10⁴, 6×10⁴, 7×10⁴, 8×10⁴, 9×10⁴, or 10×10⁴stem cells. Preferably, from about 2×10⁴ to about 3×10⁴ Passage 0 cellsare used to seed each expansion culture. The number of expansioncultures can depend upon the number of Passage 0 cells, and may begreater or fewer in number depending upon the particular placenta(s)from which the stem cells are obtained.

Expansion cultures are grown until the density of cells in culturereaches a certain value, e.g., about 1×10⁵ cells/cm². Cells can eitherbe collected and cryopreserved at this point, or passaged into newexpansion cultures as described above. Cells can be passaged, e.g., 2,3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 timesprior to use. A record of the cumulative number of population doublingsis preferably maintained during expansion culture(s). The cells from aPassage 0 culture can be expanded for 2, 3, 4, 5, 6, 7, 8, 9, 10, 12,14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38 or 40 doublings, orup to 60 doublings. Preferably, however, the number of populationdoublings, prior to dividing the population of cells into individualdoses, is between about 15 and about 30, preferably about 20 doublings.The cells can be culture continuously throughout the expansion process,or can be frozen at one or more points during expansion.

Cells to be used for individual doses can be frozen, e.g., cryopreservedfor later use. Individual doses can comprise, e.g., about 1 million toabout 100 million cells per ml, and can comprise between about 10⁶ andabout 10⁹ cells in total.

In a specific embodiment, of the method, Passage 0 cells are culturedfor approximately 4 doublings, then frozen in a first cell bank. Cellsfrom the first cell bank are frozen and used to seed a second cell bank,the cells of which are expanded for about another eight doublings. Cellsat this stage are collected and frozen and used to seed new expansioncultures that are allowed to proceed for about eight additionaldoublings, bringing the cumulative number of cell doublings to about 20.Cells at the intermediate points in passaging can be frozen in units ofabout 100,000 to about 10 million cells per ml, preferably about 1million cells per ml for use in subsequent expansion culture. Cells atabout 20 doublings can be frozen in individual doses of between about 1million to about 100 million cells per ml for administration or use inmaking a stem cell-containing composition.

In a preferred embodiment, the donor from which the placenta is obtained(e.g., the mother) is tested for at least one pathogen. If the mothertests positive for a tested pathogen, the entire lot from the placentais discarded. Such testing can be performed at any time duringproduction of placental stem cell lots, including before or afterestablishment of Passage 0 cells, or during expansion culture. Pathogensfor which the presence is tested can include, without limitation,hepatitis A, hepatitis B, hepatitis C, hepatitis D, hepatitis E, humanimmunodeficiency virus (types I and II), cytomegalovirus, herpesvirus,and the like.

In a modification of the above banks, a plurality, or all, of theplacental stem cells in a bank, e.g., placental stem cells from a singleplacenta, or from multiple placentas, are exposed to conditions thatcause differentiation of the cells into hepatocytes and/or hepatogeniccells. Such cells can be selected based on the expression of one or morehepatocyte markers not present in, or present at a detectably differentlevel in, placental stem cells. In such an embodiment, a bank of cellscan comprise populations of hepatocytes and/or hepatogenic cells, aloneor in combination with placental stem cells not differentiated tohepatocytes or hepatogenic cells.

5.7.6 Treatment of Liver Disease

In another aspect, provided herein is a method of treating a subjecthaving a disease, disorder or condition associated with abnormal liverfunction, comprising introducing a hepatocyte, or population ofhepatocytes, produced according to the methods of differentiatingplacental stem cells into hepatocytes disclosed herein, into saidsubject. In a more specific embodiment, the disease, disorder orcondition is cirrhosis of the liver. In certain embodiments, the diseaseor conditions results from liver toxicity caused by, e.g., alcohol oringestion of toxins such as, e.g., mushroom toxins. In certainembodiments, the disease or condition is a viral infection, e.g., ahepatitis A, B, C, D, or E infection.

An individual having a disease associated with abnormal liver function,e.g., an individual diagnosed with cirrhosis, can be treated with aplurality of placental stem cells, and, optionally, one or moretherapeutic agents, at any time during the progression of the disease.For example, the individual can be treated immediately after diagnosis,or within 1, 2, 3, 4, 5, 6 days of diagnosis, or within 1, 2, 3, 4, 5,6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50 or more weeks, or 1, 2,3, 4, 5, 6, 7, 8, 9, 10 or more years after diagnosis. The individualcan be treated once, or multiple times during the clinical course of thedisease. In one embodiment, the individual is administered a dose ofabout 300 million placental stem cells. Dosage, however, can varyaccording to the individual's physical characteristics, e.g., weight,and can range from 1 million to 10 billion placental stem cells perdoes, preferably between 10 million and 1 billion per dose, or between100 million and 50 million placental stem cells per dose.

The administration is preferably intravenous, but can be by anyart-accepted route for the administration of live cells. Placental stemcells, e.g., placental stem cells that have been differentiated intocells that express one or more characteristics of a hepatocyte, can betransplanted directly into one or more sites of a liver, e.g., in abuffer or medium solution, hydrogel, alginate. In one embodiment, theplacental stem cells are from a cell bank.

In another embodiment, the plurality of placental stem cells has beencontacted with one or more agents that promote differentiation of theplacental stem cells into hepatocytes or into hepatogenic cells. In sucha plurality of cells, some of the cells can be undifferentiatedplacental stem cells (i.e., placental stem cells that have not begun todifferentiate into hepatocytes); some of the cells can be placental stemcells that have begun to express one or more characteristics ofhepatocytes; and some can be cells, differentiated from placental stemcells, that have begun to express a plurality, a majority, or all of thecharacteristics of a terminally-differentiated hepatocyte.

5.7.7 Use of Placental Stem Cell-Derived Hepatocytes to IdentifyAntiviral Agents

The hepatocytes and hepatocyte cultures described herein can be used inin vitro or in vivo assays to determine whether a compound is anantiviral agent.

In vitro assays. A plurality (e.g., population) of placental stem cellscan be used to identify antiviral agents in one embodiment as follows. Apopulation of placental stem cells is established as described elsewhereherein. The population of placental stem cells is contacted with one ormore compounds or agents that promote the differentiation of theplacental stem cells into hepatocytes. The placental stem cells are thencultured until at least a plurality of the placental stem cells expressone or more markers characteristic of hepatocytes, or, in the case of,e.g., cytokeratin 18, at a level characteristic of hepatocytes.

Placenta-derived hepatocytes, or hepatogenic cells, are then infectedwith virus. The virus is preferably a virus that specifically infectshepatic tissue, e.g., hepatitis A, B, C, D or E. Virus stocks can beobtained from the serum of one or more individuals infected with thevirus who have detectable level of the virus in their serum. Virus canalso be obtained from infected animals, e.g., from infected rodents,rabbits, or the like; from commercial sources, or from cell linesinfected with the virus.

Regardless of source, the virus is contacted with the placenta-derivedhepatocytes, or population of placental stem cells comprisinghepatocytes and/or hepatogenic cells, and is given sufficient time toinfect. The hepatocytes or population of placental cells can be about,at least or at most 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 95%confluent at the time of infection, e.g., in a tissue culture dish orflask. In various embodiments, the hepatocytes or hepatogenic cells, orpopulation of hepatocytes or hepatogenic cells, differentiated fromplacental stem cells, are infected with a virus, e.g., a hepatotrophicvirus, e.g., with about 1×10⁸ to 1×10⁹ virions.

In a specific embodiment, placenta-derived hepatocytes or populations ofplacental stem cells comprising hepatocytes and/or hepatogenic cells arecollected from cell culture by trypsinization and centrifugation,washed, an resuspended in medium. Aliquots of cells are placed oncoverslips in a 12-well plate, and treated with 2% dimethylsulfoxide(DMSO) and optionally for 6-10 days. Cells are then incubated withvirions, e.g., in infected serum, at 37° C. for 10-20 hours. In anotherembodiment, placental stem cell-derived hepatocytes or populations ofplacental stem cells comprising hepatocytes and/or hepatogenic cells areinfected by co-culture with an virus-infected cells line that shedsvirus, e.g., hepatoma cell line HIB 611, which is infected with HBV (seeOchiya et al., “An In Vitro System for Infection with Hepatitis B VirusThat Uses Primary Human Fetal Hepatocytes,” Proc. Natl. Acad. Sci.U.S.A. 86:1875-1879 (1989).

At 2-5 days post-infection, the cells are collected, and the level ofvirus present is determined. Viral levels can be determined using, e.g.,one or more antibodies that recognize a viral antigen, e.g., hepatitis Avirus surface antigen (antibodies available from AbD Serotec); hepatitisB virus HBsAg of HBeAg; hepatitis C virus core antigen; hepatitis D coreantigen or hepatitis E core antigen. In another embodiment, the level ofvirus in the infected cells is determined by quantitative orsemi-quantitative PCR. In a specific embodiment, the primers used detector are specific for a replicating form of the virus, e.g., are specificfor the covalently closed circular form of HBV (cccHBV). In anotherspecific embodiment, the primers used can amplify both cccHBV and therelaxed circular form of HBV.

A compound or agent can be tested for antiviral activity at severalpoints in the above-outlined procedure. For example, the compound can becontacted with the hepatocytes or hepatogenic cells provided herein atthe time of collection from culture; after centrifugation but beforecontact with the virus; at the same time as contact with the virus(e.g., simultaneously or within minutes); or after contact with thevirus. For example, in one embodiment, contact between the compound andhepatocytes or hepatogenic cells provided herein can be accomplishedprior to infection with the virus, to determine the effect the compoundhas on initial infection. In another embodiment, the compound can becontacted with infected hepatocytes or hepatogenic cells provided hereinfrom about 1 to about 5 days after infection to determine, e.g., if thecompound has an effect on production of virus compared to cells that arenot contacted with the compound. In another embodiment, infected cellscan be contacted with the compound of interest and cocultured withuninfected hepatocytes or hepatogenic cells provided herein, or primaryhepatocyte cultures, to determine if the compound has any effect oninfection of uninfected cells.

In a specific embodiment, a compound is an antiviral compound if thecompound causes a detectable reduction in the amount of virus producedby infected hepatocytes or hepatogenic cells provided herein at anytime, e.g., within 1, 2, 3, 4, 5, 6 or 7 days after contact with thecompound, compared to hepatocytes or hepatogenic cells not contactedwith the compound. In another specific embodiment, a compound is anantiviral compound if the compound causes a detectable reduction in thenumber of infected hepatocytes in a coculture of infected hepatocytesand uninfected hepatocytes in the presence of the compound, compared toa coculture in the absence of the compound.

In vivo assays. Hepatocytes or hepatogenic cells, differentiated fromplacental stem cells, can be used as part of an in vivo assay toidentify antiviral compounds. In the assay, hepatocytes or hepatogeniccells are infected with a virus, e.g., hepatitis B virus, and implantedinto a specific mouse host to cause an initiation of viremia within themouse. A compound is then administered to the mouse, and the effects ofthe compound on the resulting viral load or viral replication isdetermined. Such an assay is described in detail in Example 10.

In one embodiment, the assays uses a normal host mouse that isirradiated with an otherwise-lethal dose of gamma irradiation, andprotected by the administration of bone marrow from an immune-restrictedmouse, e.g., a NOD/SCID mouse. At the same time as the bone marrow isadministered to the host mouse, or within 6-7 days after administrationof bone marrow, a plurality of infected placental stem cell-derivedhepatocytes or hepatogenic cells is administered to the host mouse,e.g., intraperitoneally, under the kidney capsule, into the host mouseliver, into the ear pinnae, etc. Within 6-20 days post-transplantation,a compound of interest is administered to the mouse. Such administrationcan be by any medically-acceptable route, but administration ispreferably intraperitoneal or topical.

The host mouse can be assessed an any time after administration of thecompound to determine, e.g., viral load in the serum, or for otherindicia of viral presence or replication. In various embodiments, atissue from the mouse is assayed for the presence of virions, e.greplicating forms of the virus. As above, viral levels can be determinedusing, e.g., one or more antibodies that recognize a viral antigen,e.g., hepatitis A virus surface antigen (antibodies available from AbDSerotec); hepatitis B virus HBsAg of HBeAg; hepatitis C virus coreantigen; hepatitis D core antigen or hepatitis E core antigen. In aspecific embodiment, for example, the presence of hepatitis B virus in aserum sample from a host mouse is detected using one or more antibodiesto a hepatitis B virus envelope protein, surface antigen, or coreantigen. In another embodiment, the level of virus in the infected cellsis determined by quantitative or semi-quantitative PCR. In a specificembodiment, the primers used detect or are specific for a replicatingform of the virus, e.g., are specific for the covalently closed circularform of HBV (cccHBV). In another specific embodiment, the primers usedcan amplify both cccHBV and the relaxed circular form of HBV.

5.7.8 Treatment of Cartilage Damage

In other embodiments, isolated placental stem cells, isolatedpopulations of placental stem cells, and/or chondrocytic cells orchondrocytes differentiated therefrom, may be used in autologous orallogeneic tissue regeneration or replacement therapies or protocols,including, but not limited to repair of cartilage tissue. In a specificembodiment, placental stem cells can be used to heal or repair adisease, disorder or condition affecting cartilage, including trauma tocartilage (e.g., breaks, tears, etc.). In a more specific embodiment,the cartilage is articular cartilage. Placental stem cells can beadministered to the cartilage directly, e.g., in a cell suspension, orcan be administered to the cartilage in combination with a matrix, e.g.,an electrospun nanofibrous scaffold, such as electrospun nanofibrousscaffolds described in Section 5.7.1.4, above. Placental stem cellscontacted with (e.g., seeded onto) to the cartilage, with or without ascaffold, are preferably CD200⁺, CD105′, CD90⁺, CD34⁻, CD45⁻ placentalstem cells, but can be any of the placental stem cells described herein.All or a plurality of the placental stem cells used to treat a disease,disorder or condition in cartilage can be differentiated to chondrocyticcells prior to administration to the cartilage, or can be administeredin an undifferentiated state. The chondrocytic cells or chondrocytes canbe administered alone, or in combination with placental stem cellsand/or another type of stem cell, in a cell suspension, or can beadministered to the cartilage in combination with a matrix, e.g., anelectrospun nanofibrous scaffold.

The effectiveness of a particular population of placental stem cells,alone or in combination with a scaffold, e.g., an electrospunnanofibrous scaffold, can be evaluated in an animal model that does notspontaneously heal a cartilage injury, e.g., a rabbit osteochondraldefect model, e.g., as described in Example 14, below.

5.7.9 Uses of CD34⁺, CD45⁻ Placental Stem Cells

CD34⁺, CD45⁻ placental stem cells, and cell populations enriched forCD34⁺, CD45⁻ placental stem cells, provided herein can be used to treatan individual in need of hematopoietic stem cells, e.g., an individualin need of hematopoietic reconstitution, for example, after chemotherapyor myeloablation. In one embodiment, placental CD34⁺CD45⁻ stem cellsalone are used to treat such an individual. In another embodiment,placental CD34⁺CD45⁻ stem cells are used in combination with, or tosupplement, a second type of stem cell, or a second population of stemcells. Stem cells in such a second population can comprise hematopoieticstem cells, non-hematopoietic stem cells, or both. In one embodiment,the second population of stem cells comprises stem cells in cord blood.In another embodiment, the second population of stem cells comprisesstem cells in bone marrow. In a specific embodiment, the stem cells aretransplanted into the individual.

Typically, a patient receiving a stem cell infusion, for example for abone marrow transplantation, receives one unit of nucleated cells, wherea unit is approximately 1×10⁹ nucleated cells (corresponding to 1-2×10⁶CD34⁺ stem cells). Thus, in one embodiment, the number of nucleatedcells, comprising CD34⁺CD45⁻ placental stem cells, administered to anindividual, is at least five times the number of cells normallyadministered in a bone marrow replacement. In another specificembodiment of the method, the number of nucleated cells administered toan individual is at least ten times the number of cells normallyadministered in a bone marrow replacement. In another specificembodiment, the number of nucleated cells administered to an individualis at least fifteen times the number of cells normally administered in abone marrow replacement. In another embodiment of the method, the totalnumber of nucleated cells, which includes CD34⁺CD45⁻ placental stemcells, administered to an individual is between 1-1000×10⁸ per kilogramof body weight.

In other embodiments, CD34⁺CD45⁻ placental stem cells, e.g., a cellpopulation enriched in CD34⁺CD45⁻ placental stem cells, improvesengraftment in an individual in need of stem cells, e.g., hematopoieticstem cells, compared to engraftment in an individual not receiving apopulation of hematopoietic stem cells enriched in CD34⁺CD45⁻ placentalstem cells. In various embodiments, the engraftment is improved atleast, or at, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,18, 19, 20 or 21 days post-transplant. In another more specificembodiment, CD34⁺CD45⁻ placental stem cells improve engraftment in anindividual in need of stem cells at least, or at, more than 21 dayspost-transplant. In specific embodiments, CD34⁺CD45⁻ placental stemcells improves engraftment in an individual in need of stem cells atleast, or at, more than 25, 30, 35, 40, 45, 50, 55 weeks, or 1 year orlonger post-transplant.

The CD34⁺CD45⁻ placental stem cells, and populations of stem cellscomprising such stem cells, can be prepared in a form that is easilyadministrable to an individual. For example, the cells or cellpopulation can be contained within a container suitable for medical use.Such a container can be, for example, a sterile plastic bag, flask, jar,or other container from which the combined stem cell population can beeasily dispensed. Preferably, the container is a container that allows,or facilitates, intravenous administration of a combined stem cellpopulation. The container, e.g., bag, can hold the placenta-derived stemcells and stem cells from a second source together, e.g., as a mixedcell population, or can hold the two stem cell populations separately.In the latter embodiment, the bag preferably comprises multiple lumensor compartments that are interconnected to allow mixing of theplacenta-derived stem cells and stem cells from a second source priorto, or during, administration. The container is preferably one thatallows for cryopreservation of the combined stem cell population.

Thus, in one embodiment, provided herein is a composition comprising aCD34⁺CD45⁻ placental stem cell-enriched cell population in a container.In another embodiment, provided herein is a composition comprising astem cell population, wherein said stem cell population comprisesCD34⁺CD45⁻ placenta-derived stem cells and second type of stem cells ina container. In a specific embodiment, the container is a bag, flask, orjar. In a more specific embodiment, said placenta-derived stem cells andsaid second type of stem cells are contained together in said bag. Inanother more specific embodiment, said placenta-derived stem cells andsaid second type of stem cells from a second source are containedseparately within said bag. In another specific embodiment, thecomposition comprises one or more compounds that facilitatecryopreservation of the combined stem cell population. In anotherspecific embodiment, said combined stem cell population is containedwithin a physiologically-acceptable aqueous solution. In a more specificembodiment, said physiologically-acceptable aqueous solution is a 0.9%NaCl solution. In another more specific embodiment, said bag is asterile plastic bag. In a more specific embodiment, said bag allows orfacilitates intravenous administration of said stem cells. In anotherspecific embodiment, the stem cells comprise CD34⁺CD45⁻ placental cellsthat are HLA-matched to said stem cells from a second source. In anotherspecific embodiment, stem cells comprise CD34⁺CD45⁻ placental stem cellsthat are at least partially HLA-mismatched to the second type of stemcell. In another specific embodiment, said placenta-derived stem cellsare derived from a plurality of donors. In another specific embodiment,said stem cells from a second source are derived from a plurality ofdonors.

CD34⁺CD45⁻ stem cells and cell populations comprising CD34⁺CD45⁻placental stem cells can be cultured for a period of time prior toadministration to an individual. For example, in one embodiment, thestem cells can be cultured in medium comprising Notch agonist, e.g., adeletion form of a Notch protein consisting essentially of theintracellular domain of the Notch protein, or a Delta protein. See U.S.2004/0067583.

In another embodiment, a population of CD34⁺CD45⁻ placental stem cellsprovided herein and a population of umbilical cord blood cells areadministered sequentially to a patient in need thereof. In oneembodiment, the population of placental stem cells is administered firstand the population of stem cells of a second type is administeredsecond. In another embodiment, the stem cells of a second type areadministered first and the CD34⁺CD45⁻ placental stem cells areadministered second.

Combined populations of CD34⁺CD45⁻ placental stem cells, and stem cellsof a second type, e.g., cord blood-derived stem or progenitor cells, orcord blood, including banked or cryopreserved cord blood, can be mixed,prior to transplantation, by any medically-acceptable means. In oneembodiment, the two populations are physically mixed. In anotherembodiment of the method, populations are mixed immediately prior to(i.e., within 1, 2, 3, 4, 5, 7, 10 minutes of) administration to saidindividual. In another embodiment, populations are mixed at a point intime more than five minutes prior to administration to said individual.In another embodiment of the method, the CD34⁺CD45⁻ placental stemcells, and/or stem cells of a second type, are cryopreserved and thawedprior to administration to said individual. In another embodiment, stemcells are mixed at a point in time more than 1, 2, 3, 4, 5, 6, 7, 8, 9,10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, or 24 hoursprior to administration to said individual, wherein either or both ofthe populations of stem cells have been cryopreserved and thawed priorto said administration. In another embodiment, the stem cell populationsmay be administered more than once.

In another embodiment, the CD34⁺CD45⁻ placental stem cells and/or stemcells of a second type are preconditioned prior to transplantation. In apreferred embodiment, preconditioning comprises storing the cells in agas-permeable container generally for a period of time at about −5° C.to about 23° C., about 0° C. to about 10° C., or preferably about 4° C.to about 5° C. The cells may be stored between 18 hours and 21 days,between 48 hours and 10 days, preferably between 3-5 days. The cells maybe cryopreserved prior to preconditioning or, may be preconditionedimmediately prior to administration.

Either or both of the CD34 CD45⁻ placental stem cells, or stem cells ofa second type, may be differentiated prior to contacting an individualin need of stem cells. For example, for contacting for the purpose ofhematopoietic engraftment, the stem cells may be differentiated to cellsin the hematopoietic lineage. In certain embodiments, the method oftransplantation of stem cell populations comprises (a) induction ofdifferentiation of the CD34⁺CD45⁻ placental stem cells, (b) mixing theplacental stem cells with a population of stem cells of a second type,e.g., cord blood stem cells, to form a combined cell population, and (c)administration of the combined cell population to an individual in needthereof. In another embodiment the method of transplantation comprises(a) induction of differentiation of stem cells of a second type; (b)mixing the differentiated cells with CD34⁺CD45⁻ placental stem cells toform a combined cell population; and (c) administration of the combinedcell population to an individual in need thereof. In another embodiment,the method of transplantation of combined stem cell populationscomprises (a) mixing CD34⁺CD45⁻ placental stem cells with a populationof cord blood cells; (b) induction of differentiation of the mixture ofthe cord blood cells and CD34′CD45⁻ placental stem cells and (c)administration of the mixture to a patient in need thereof.

The stem cell populations provided herein, enriched for CD34⁺CD45⁻placental stem cells, may be transplanted into a patient in anypharmaceutically or medically acceptable manner, including by injection,e.g., intravenous injection, intramuscular injection, intraperitonealinjection, intraocular injection, direct injection into a particulartissue, transfusion, etc. For example, combined stem cell populations,e.g., placental stem cells in combination with cord blood-derived stemcells) may be transplanted by intravenous infusion. In anotherembodiment, a combined stem cell population comprising placental stemcells and cardiac stem cells, in suspension, may be injected directlyinto cardiac tissue, e.g., an ischemic area in a heart. The combinedstem cell populations may comprise, or be suspended in, anypharmaceutically-acceptable carrier. The combined stem cell populationsmay be carried, stored, or transported in any pharmaceutically ormedically acceptable container, for example, a blood bag, transfer bag,plastic tube or vial.

After transplantation, engraftment in a human recipient may be assessedusing, e.g., nucleic acid or protein detection or analytical methods.For example, the polymerase chain reaction (PCR), STR, SSCP, RFLPanalysis, AFLP analysis, and the like, may be used to identify engraftedcell-specific nucleotide sequences in a tissue sample from therecipient. Such nucleic acid detection and analysis methods arewell-known in the art. In one embodiment, engraftment may be determinedby the appearance of engrafted cell-specific nucleic acids in a tissuesample from a recipient, which are distinguishable from background. Thetissue sample analyzed may be, for example, a biopsy (e.g., bone marrowaspirate) or a blood sample.

In one embodiment, a sample of peripheral blood is taken from a patientimmediately prior to a medical procedure, e.g., myeloablation. After theprocedure, a combined stem cell as provided herein is administered tothe patient. At least once post-administration, a second sample ofperipheral blood is taken. An STR profile is obtained for both samples,e.g., using PCR primers for markers (alleles) available from, e.g.,LabCorp (Laboratory Corporation of America). A difference in the numberor characteristics of the markers (alleles) post-administrationindicates that engraftment has taken place.

Engraftment can also be demonstrated by detection of re-emergence ofneutrophils.

In another example, engrafted cell-specific markers may be detected in atissue sample from the recipient using antibodies directed to markersspecific to either the transplanted stem cells, or cells into which thetransplanted stem cells would be expected to differentiate. In oneembodiment, engraftment of a combination of placental stem cells andcord blood-derived stem cells may be assessed by FACS analysis todetermine the presence of CD45⁺, CD19⁺, CD33′, CD7⁺ and/or CD3⁺ cells byadding the appropriate antibody and allowing binding; washing (e.g.,with PBS); fixing the cells (e.g., with 1% paraformaldehyde); andanalyzing on an appropriate FACS apparatus (e.g., a FACSCalibur flowcytometer (Becton Dickinson)). Where placental stem cells and/or steincells from a second source are from an individual of a different sexthan a recipient, e.g., male donor and female recipient, engraftment canbe determined by detection of sex-specific markers, e.g.,Y-chromosome-specific markers. Placental stem cells and/or stem cellsfrom a second source may also be genetically modified to express aunique marker or nucleic acid sequence that facilitates identification,e.g., an RFLP marker, expression of β-galactosidase or green fluorescentprotein, or the like.

The degree of engraftment may be assessed by any means known in the art.In one embodiment, the degree of engraftment is assessed by a gradingsystem as follows, which uses a thin section of fixed and antibody-boundtissue from the transplant recipient. In this example grading system,engraftment is graded as follows: 0=no positive cells (that is, no cellsbound by an antibody specific to an engrafted cell); 0.5=one or twopositive cells, perhaps positive, but difficult to differentiate frombackground or non-specific staining; 1=2-20 scattered positive cells;2=approximately 20-100 scattered or clustered positive cells throughoutthe tissue; 3=more than 100 positive cells comprising less than 50% ofthe tissue; 4=more than 50% of cells are positive. In specificembodiments, engraftment is determined where greater than 0.5%, 1%, 2%,3%, 4%, 5%, 7.5%, 10%, 15%, 20% or greater of the cells are positivelystained.

In another embodiment, the degree of engraftment is determined byanalysis of the gain of one or more biological functions carried out bythe engrafted cells. For example, where a recipient, who has undergonemyeloablative therapy, receives a transplant of a combined stem cellpopulation comprising placental stem cells and cord blood-derived stemcells, the degree of engraftment may be determined by the degree towhich normal hematopoiesis, blood cell populations and blood functionreturn to normal.

Where the combined stem cell population in whole or in part isHLA-mismatched to an intended recipient, it may be necessary to treatthe recipient to reduce immunological rejection of the donor cells.Methods for reducing immunological rejection are disclosed in, e.g.,U.S. Pat. Nos. 5,800,539 and 5,806,529, both of which are incorporatedherein by reference.

In one embodiment, therefore, combined stem cell populations comprisinghematopoietic stem cells can be used to treat patients having a bloodcancer, such as a lymphoma, leukemia (such as chronic or acutemyelogenous leukemia, acute lymphocytic leukemia, Hodgkin's disease,etc.), myelodysplasia, myelodysplastic syndrome, and the like. Inanother embodiment, the disease, disorder or condition is chronicgranulomatous disease.

Because hematopoietic reconstitution can be used in the treatment ofanemias, further provided herein is the treatment of an individual withCD34⁺CD45⁻ placental stem cells of the invention, wherein the individualhas an anemia or disorder of the blood hemoglobin. The anemia ordisorder may be natural (e.g., caused by genetics or disease), or may beartificially-induced (e.g., by accidental or deliberate poisoning,chemotherapy, and the like). In another embodiment, the disease ordisorder is a marrow failure syndrome (e.g., aplastic anemia, Kostmannsyndrome, Diamond-Blackfan anemia, amegakaryocytic thrombocytopenia, andthe like), a bone marrow disorder or a hematopoietic disease ordisorder. In a specific embodiment, the CD34⁺CD45⁻ placental stem cellsare administered with a plurality of mesenchymal stem cells and/or aplurality of adherent placental stem cells.

In another embodiment, the CD34⁺CD45⁻ placental stem cells providedherein can be introduced, alone or in combination with a second type ofstem cell, e.g., a mesenchymal stem cell or an adherent placental stemcell, into a damaged organ for organ neogenesis and repair of injury invivo. Such injury may be due to conditions and disorders including, butnot limited to, myocardial infarction, seizure disorder, multiplesclerosis, stroke, hypotension, cardiac arrest, ischemia, inflammation,age-related loss of cognitive function, cerebral palsy,neurodegenerative disease, Alzheimer's disease, Parkinson's disease,Leigh disease, AIDS dementia, memory loss, amyotrophic lateralsclerosis, ischemic renal disease, brain or spinal cord trauma,heart-lung bypass, glaucoma, retinal ischemia, or retinal trauma.

In other embodiments, the disease, disorder or condition includes, butis not limited to lysosomal storage diseases, such as Tay-Sachs,Niemann-Pick, Fabry's, Gaucher's disease (e.g., glucocerebrosidasedeficiency), Hunter's, and Hurler's syndromes, Maroteaux-Lamy syndrome,fucosidosis (fucosidase deficiency), Batten disease (CLN3), as well asother gangliosidoses, mucopolysaccharidoses, and glycogenoses.

In other embodiments, the CD34⁺CD45⁻ placental stem cells providedherein can be used as autologous or heterologous transgene carriers ingene therapy to correct, for example, inborn errors of metabolism,adrenoleukodystrophy (e.g., co-A ligase deficiency), metachromaticleukodystrophy (arylsulfatase A deficiency) (e.g., symptomatic, orpresymptomatic late infantile or juvenile forms), globoid cellleukodystrophy (Krabbe's disease; galactocerebrosidase deficiency), acidlipase deficiency (Wolman disease), cystic fibrosis, glycogen storagedisease, hypothyroidism, sickle cell anemia, thalassemia (e.g., betathalassemia), Pearson syndrome, Pompe's disease, phenylketonuria (PKU),porphyrias, maple syrup urine disease, homocystinuria,mucoplysaccharidosis, chronic granulomatous disease and tyrosinemia andTay-Sachs disease or to treat solid tumors or other pathologicalconditions.

In other embodiments, the disease, disorder or condition is a disease,disorder or condition requiring replacement or repair of one or moretissues. For example, the CD34⁺ CD45⁻ placental stem cells providedherein, alone or in combination with a second type of stem cell, e.g., amesenchymal stein cell or an adherent placental stem cell, can be usedin therapeutic transplantation protocols, e.g., to augment or replacestem or progenitor cells of the liver, pancreas, kidney, lung, nervoussystem, muscular system, bone, bone marrow, thymus, spleen, mucosaltissue, gonads, or hair. The combined stem cell populations providedherein can also be used for augmentation, repair or replacement of,e.g., cartilage, tendon, or ligaments. For example, in certainembodiments, prostheses (e.g., hip prostheses) are coated withreplacement cartilage tissue constructs grown from combined stem cellpopulations provided herein. In other embodiments, joints (e.g., knee)are reconstructed with cartilage tissue constructs grown from combinedstem cell populations. Cartilage tissue constructs can also be employedin major reconstructive surgery for different types of joints (forprotocols, see e.g., Resnick, D., and Niwayama, G., eds., 1988,DIAGNOSIS OF BONE AND JOINT DISORDERS, 2D ED., W. B. Saunders Co.). Thecombined stem cell populations can be used to repair damage of tissuesand organs resulting from trauma, metabolic disorders, or disease. Inone embodiment, a patient can be administered a combined stem cellpopulation to regenerate or restore tissues or organs which have beendamaged as a consequence of disease, e.g., to repair heart tissuefollowing myocardial infarction.

In another embodiment, the CD34⁺CD45⁻ placental stem cells providedherein, alone or in combination with a second type of stem cell, e.g., amesenchymal stem cell or an adherent placental stem cell, may be used totreat an individual who has received a lethal or sub-lethal dose ofradiation. Such radiation may be accidentally received, for example in anuclear incident, whether work- or aggression-related, or therapeutic,for example, as part of a medical procedure. The particular type ofradiation (e.g., alpha, beta, gamma) is not critical. The combined stemcell populations provided herein may be used to ameliorate one or moresymptoms of radiation sickness, for example, nausea, loss of appetite,lethargy, dyspnea, decreased white blood cell count, chronic anemia,fatigue, weakness, paleness, difficulty breathing, feelings of malaise,and the like, whether such symptoms are indicative of recoverable orfatal radiation sickness. In another embodiment, the individual has oneor more symptoms associated with acute radiation syndrome (ARS). Thecombined stem cell populations provided herein may also be used topartially or fully reconstitute the hematopoietic system of anindividual that has received a lethal or sub-lethal dose of radiation,such that the individual becomes partially or fully chimeric. Suchchimerism may be temporary or permanent (e.g., may persist for 1, 2, 3weeks, or 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 months or longer). In apreferred embodiment, a combined stem cell population provided herein isprovided to the individual within the first 24 hours after exposure. Theindividual may be administered a combined stem cell population withinthe first hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 9 hours, 12hours, 15 hours, 18 hours, or 21 hours after exposure to radiation. Acombined stem cell population as provided herein may also beadministered within 2 days, 3 days, 4 days, 5 days, 6 days, one week, 2weeks, 3 weeks, 4 weeks or 5 weeks after exposure to radiation.

Therapeutic or prophylactic treatment of an individual with theCD34⁺CD45⁻ placental stem cells provided herein may be consideredeffective if the disease, disorder or condition is measurably improvedin any way. Such improvement may be shown by a number of indicators.Measurable indicators include, for example, detectable changes in aphysiological condition or set of physiological conditions associatedwith a particular disease, disorder or condition (including, but notlimited to, blood pressure, heart rate, respiratory rate, counts ofvarious blood cell types, levels in the blood of certain proteins,carbohydrates, lipids or cytokines or modulation expression of geneticmarkers associated with the disease, disorder or condition). Treatmentof an individual with the CD34⁺CD45⁻ placental stem cells providedherein would be considered effective if any one of such indicatorsresponds to such treatment by changing to a value that is within, orcloser to, the normal value. The normal value may be established bynormal ranges that are known in the art for various indicators, or bycomparison to such values in a control. Introduction of a combined stemcell population as provided herein for the purposes of engraftment,e.g., hematopoietic engraftment, would be considered successful if theindividual to whom the combined stem cell population is introducedexhibits any indications of engraftment (e.g., markers of engraftedcells appearing in biopsy or tissue samples, or blood sample; detectionof one or more biochemical functions performed by the engrafted cells,etc.). In medical science, the efficacy of a treatment is also oftencharacterized in terms of an individual's impressions and subjectivefeeling of the individual's state of health. Improvement therefore mayalso be characterized by subjective indicators, such as the individual'ssubjective feeling of improvement, increased well-being, increased stateof health, improved level of energy, or the like, after administrationof the stem cells or supplemented cell populations provided herein.

6. EXAMPLES 6.1 Example 1: Obtaining Placental Stem Cells

6.1.1 Tissue Disruption/Enzymatic Digestion

An exemplary protocol for obtaining stem cells from placental tissue byenzymatic digestion is as follows. Frozen placental tissue (three piecesof approximately −1×1×0.5 cm each) is obtained. The tissue is umbilicalcord, maternal surface of the placenta, or amniotic membrane. Digestiveenzymes used include trypsin-EDTA (0.25%, GIBCO BRL); collagenase IA(Sigma), collagenase I (Worthington), collagenase IA(Sigma)+Trypsin-EDTA, collagenase 1 (Worthington)+Trypsin-EDTA, orElastase+Collagenase I+Collagenase IV+Daspase (Worthington). Digestionof placental tissue is as follows. Tissue is minced in the presence ofenzymes (1 g in 10 ml in 50 ml tube) at 37° C., 250 rpm shaking, tubeposition at 45° angle for 1 hr (C25 Incubator Shaker, New BrunswickScientific, Edison, N.J., USA). The supernatant is then discarded. Thepellet is washed with 20 ml Hank's+5% FCS (3 times), and re-suspended in12 ml culture medium. 3 ml of the resulting suspension are aliquotedinto T-75 flasks containing 10 ml culture medium each (four flasks perdigestion). Optionally, 10 ml Trypsin/EDTA is added for 30 min at 37°C., with shaking at 250 rpm, with recentrifugation and an additionalwash with 10 ml Hank's+5% FCS. Cells are plated and cultured, selectingfor adherent cells.

The following method may also be used. A placenta is obtained less than24 hours after expulsion. After cleaning the placenta, a hemostat isclamped to the distal end of the umbilical cord. The umbilical cord iscut at the junction with the placenta and transferred to a sterile dish.After cutting the cord below the hemostat, the cord is massaged toremove blood clots, and transferred to 500 ml PBS containing gentamicinand amphotericin B. 5 g of this cord is used. A scalpel is used to trimthe remaining placental material by cutting in a radius of about 3inches from the umbilical cord attachment point. Blood clots are forcedfrom the remaining material, and 5 g of the amnion-chorion, centered atthe umbilical cord root, is transferred to the same container as theumbilical cord. The umbilical cord and amnion-chorion tissue is sliced,then minced to pieces about 1 mm³ in size. The tissue is then digestedwith 1 mg/ml Collagenase 1A (20 ml/g tissue) for 1 hour at 37° C.followed by Trypsin-EDTA (10 ml/g tissue) for 30 minutes at 37° C. Afterthree washes in 5% FBS in PBS, the tissue is resuspended in culturemedium (20 ml/g tissue) and transferred to T flasks at about 0.22ml/cm².

6.1.2 Perfusion

A post-partum placenta is obtained within 24 hours after birth. Theumbilical cord is clamped with an umbilical cord clamp approximately 3to 4 inches about the placental disk, and the cord is cut above theclamp. The umbilical cord is either discarded, or processed to recover,e.g., umbilical cord stem cells, and/or to process the umbilical cordmembrane for the production of a biomaterial. Excess amniotic membraneand chorion is cut from the placenta, leaving approximately ¼ incharound the edge of the placenta. The trimmed material is discarded.

Starting from the edge of the placental membrane, the amniotic membraneis separated from the chorion using blunt dissection with the fingers.When the amniotic membrane is entirely separated from the chorion, theamniotic membrane is cut around the base of the umbilical cord withscissors, and detached from the placental disk. The amniotic membranecan be discarded, or processed, e.g., to obtain stem cells by enzymaticdigestion, or to produce, e.g., an amniotic membrane biomaterial.

The fetal side of the remaining placental material is cleaned of allvisible blood clots and residual blood using sterile gauze, and is thensterilized by wiping with an iodine swab than with an alcohol swab. Theumbilical cord is then clamped crosswise with a sterile hemostat beneaththe umbilical cord clamp, and the hemostat is rotated away, pulling thecord over the clamp to create a fold. The cord is then partially cutbelow the hemostat to expose a cross-section of the cord supported bythe clamp. Alternatively, the cord is clamped with a sterile hemostat.The cord is then placed on sterile gauze and held with the hemostat toprovide tension. The cord is then cut straight across directly below thehemostat, and the edge of the cord near the vessel is re-clamped.

The vessels exposed as described above, usually a vein and two arteries,are identified, and opened as follows. A closed alligator clamp isadvanced through the cut end of each vessel, taking care not to puncturethe clamp through the vessel wall. Insertion is halted when the tip ofthe clamp is slightly above the base of the umbilical cord. The clamp isthen slightly opened, and slowly withdrawn from the vessel to dilate thevessel.

Plastic tubing, connected to a perfusion device or peristaltic pump, isinserted into each of the placental arteries. Plastic tubing, connectedto a 250 mL collection bag, is inserted into the placental vein. Thetubing is taped into place.

A small volume of sterile injection grade 0.9% NaCl solution to checkfor leaks. If no leaks are present, the pump speed is increased, andabout 750 mL of the injection grade 0.9% NaCl solution is pumped throughthe placental vasculature. Perfusion can be aided by gently massagingthe placental disk from the outer edges to the cord. When a collectionbag is full, the bag is removed from the coupler connecting the tubingto the bag, and a new bag is connected to the tube.

When collection is finished, the collection bags are weighed andbalanced for centrifugation. After centrifugation. each bag is placedinside a plasma extractor without disturbing the pellet of cells. Thesupernatant within the bags is then removed and discarded. The bag isthen gently massaged to resuspend the cells in the remainingsupernatant. Using a sterile 1 mL syringe, about 300-500 μL of cells iswithdrawn from the collection bag, via a sampling site coupler, andtransferred to a 1.5 mL centrifuge tube. The weight and volume of theremaining perfusate are determined, and ⅓ volume of hetastarch is addedto the perfusate and mixed thoroughly. The number of cells per mL isdetermined. Red blood cells are removed from the perfusate using aplasma extractor.

Placental cells are then immediately cultured to isolate placental stemcells, or are cryopreserved for later use.

6.1.3 Culture of Isolated Stem Cells

Primary Culture:

The purpose of primary culture is to establish cells from digestedplacental tissue. The digested tissue is suspended in culture medium andplaced into Corning T-flasks, which are incubated in a humidifiedchamber maintained at 37° C. with 5% CO₂. Half of the medium isreplenished after 5 days of culture. High-density colonies of cells formby 2 weeks of culture. Colonies are harvested with Trypsin-EDTA, whichis then quenched with 2% FBS in PBS. Cells are centrifuged andresuspended in culture medium for seeding expansion cultures. Thesecells are defined as Passage 0 cells having doubled 0 times.

Expansion Culture:

Cells harvested from primary culture, harvested from expansion culture,or thawed from the cell bank are used to seed expansion cultures. CellFactories (NUNC™) are treated with 5% CO₂ in air at 50 ml/min/tray for10 min through a sterile filter and warmed in a humidified incubatormaintained at 37° C. with 5% CO₂. Cell seeds are counted on ahemacytometer with trypan blue, and cell number, viability, passagenumber, and the cumulative number of doublings are recorded. Cells aresuspended in culture medium to about 2.3×10⁴ cells/ml and 110 ml/trayare seeded in the Cell Factories. After 3-4 days and again at 5-6 daysof culture, culture medium is removed and replaced with fresh medium,followed by another treatment with 5% CO₂ in air. When cells reachapproximately 10⁵ cells/cm², cells are harvested with Trypsin-EDTA,followed by quenching with 2% FBS in PBS. Cell are then centrifuged andresuspended in culture medium.

6.2 Example 2: Isolation and Characterization of Placental Stem Cellsfrom Perfusate

This Example demonstrates the collection and characterization ofplacental stem cells from several different perfusion experiments.

Materials and Methods

Placenta donors were recruited from expectant mothers that enrolled inprivate umbilical cord blood banking programs and provided informedconsent permitting the use of the exsanguinated placenta followingrecovery of cord blood for research purposes. These donors alsopermitted use of blinded data generated from the normal processing oftheir umbilical cord blood specimens for cryopreservation. This allowedcomparison between the composition of the collected cord blood and theeffluent perfusate recovered using this experimental method describedbelow. All donor data was kept confidential.

Following exsanguination of the umbilical cord and placenta, theplacenta was placed in a sterile, insulated container at roomtemperature and delivered to the laboratory within 4 hours of birth.Placentas were discarded if, on inspection, they had evidence ofphysical damage such as fragmentation of the organ or avulsion ofumbilical vessels. Placentas were maintained at room temperature (23±2°C.) or refrigerated (4° C.) in sterile containers for 2 to 20 hours.Periodically, the placentas were immersed and washed in sterile salineat 25±3° C. to remove any visible surface blood or debris. The umbilicalcord was transected approximately 5 cm from its insertion into theplacenta and the umbilical vessels were cannulated with Teflon orpolypropylene catheters connected to a sterile fluid path allowingbidirectional perfusion of the placenta and recovery of the effluentfluid.

Placental Conditioning

Placentas were obtained from delivery rooms along with cord blood afterobtaining written parental consent, and were processed at roomtemperature within 12 to 24 hours after delivery. Before processing, themembranes were removed and the maternal site washed clean of residualblood. The placenta was maintained under varying conditions in anattempt to simulate and sustain a physiologically compatible environmentfor the proliferation and recruitment of residual cells. The umbilicalvessels were cannulated with catheters made from 20 gauge Butterflyneedles use for blood sample collection. The cannula was flushed withIMDM serum-free medium (GibcoBRL, NY) containing 2 U/ml heparin(EJkins-Sinn, N.J.). Placentas were then perfused with heparinized (2U/mL) Dulbecco's modified Eagle Medium (DMEM) at the rate of 15mL/minute for 10 minutes and the perfusates were collected from thematernal sites within one hour and the nucleated cells counted.Perfusion of the placenta continued at a rate of 50 mL per minute untilapproximately 150 mL of perfusate was collected. This volume ofperfusate was labeled “early fraction”. The perfusion and collectionprocedures were repeated once or twice until the number of recoverednucleated cells fell below 100/microL. Continued perfusion of theplacenta at the same rate resulted in the collection of a secondfraction of approximately 150 mL and was labeled “late fraction”. Duringthe course of the procedure, the placenta was gently massaged to aid inthe perfusion process and assist in the recovery of cellular material.Effluent fluid was collected from the perfusion circuit by both gravitydrainage and aspiration through the arterial cannula.

The perfusates were pooled and subjected to light centrifugation toremove platelets, debris and denucleated cell membranes. The nucleatedcells were then isolated by Ficoll-Hypaque density gradientcentrifugation and after washing, resuspended in DMEM. For isolation ofthe adherent cells, aliquots of 5-10×10⁶ cells were placed in each ofseveral T-75 flasks and cultured with commercially available MesenchymalStem Cell Growth Medium (MSCGM) obtained from BioWhittaker, and placedin a tissue culture incubator (37° C., 5% CO₂). After 10 to 15 days,non-adherent cells were removed by washing with PBS, which was thenreplaced by MSCGM. The flasks were examined daily for the presence ofvarious adherent cell types and in particular, for identification andexpansion of clusters of adherent fibroblastoid cells.

Cell Recovery and Isolation

Cells were recovered from the perfusates by centrifugation at 400×g for15 minutes at room temperature. The cell pellets were resuspended inIMDM serum-free medium containing 2 U/ml heparin and 2 mM EDTA(GibcoBRL, NY). The total mononuclear cell fraction was isolated usingLYMPHOPREP™ (Nycomed Pharma, Oslo, Norway) according to themanufacturer's recommended procedure and the mononuclear cell fractionwas resuspended. Cells were counted using a hemocytometer. Viability wasevaluated by trypan blue exclusion. Isolation of mesenchymal cells wasachieved by differential trypsinization using a solution of 0.05%trypsin with 0.2% EDTA (Sigma). Differential trypsinization was possiblebecause fibroblastoid cells, including adherent placental stem cells,detached from plastic surfaces within about five minutes whereas otheradherent populations required more than 20-30 minutes incubation.

The detached fibroblastoid cells were harvested following trypsinizationand trypsin neutralization, using Trypsin Neutralyzing Solution (TNS,BioWhitaker). The cells were washed in DMEM and resuspended in MSCGM.Flow cytometry was carried out using a Becton-Dickinson FACSCaliburinstrument and FITC and PE labeled monoclonal antibodies, selected onthe basis of known markers for bone marrow-derived MSC (mesenchymal stemcells), including antibodies to CD10, CD34, CD44, CD45 and CD90.Antibodies were purchased from Becton-Dickinson and Caltag laboratories(South San Francisco, Calif.), and SH2, SH3 and SH4 antibody-producinghybridomas were obtained from the American Type Culture Collection.Reactivities of the MoAbs in their cultured supernatants were detectedby FITC or PE labeled F(ab)′₂ goat anti-mouse antibodies. Lineagedifferentiation was carried out using the commercially availableinduction and maintenance culture media (BioWhittaker), used as permanufacturer's instructions.

Isolation of Placental Stem Cells

Microscopic examination of the adherent cells in the culture flasksrevealed morphologically different cell types, including spindle-shapedcells; round cells with large nuclei and numerous perinuclear smallvacuoles; and star-shaped cells with several projections, through one ofwhich the cells were attached to the flask. Although no attempts weremade to further characterize these adherent cells, similar cells wereobserved in the culture of bone marrow, cord and peripheral blood, andtherefore considered to be non-stem cell in nature.

Fibroblastoid adherent cells, appearing as clusters, were similar inappearance to mesenchymal stem cells (MSC), and were isolated bydifferential trypsinization and subcultured in secondary flasks. Thecells appeared rounded after trypsinization. Phase microscopy of therounded cells, after trypsinization, showed the cells to be highlygranulated and similar to bone marrow-derived MSC produced in thelaboratory or purchased from commercial sources, e.g., BioWhittaker.When subcultured, the adherent placental cells, in contrast to theirearlier phase, adhered within hours, assumed the characteristicfibroblastoid shape, and formed a growth pattern similar to thereference bone marrow-derived MSC. Moreover, during subculturing andrefeeding, loosely bound mononuclear cells were washed out and thecultures remained homogeneous and devoid of any visiblenon-fibroblastoid cell contaminants.

Flow Cytometry

The expression of CD34, CD38, SH2, SH3, SH4 and other stemcell-associated surface markers on early and late fraction purifiedmononuclear cells was assessed by flow cytometry. In a specific case,cells were washed in PBS and then double-stained with anti-CD34phycoerythrin and anti-CD38 fluorescein isothiocyanate (BectonDickinson, Mountain View, Calif.).

In separate experiments, placental stem cells obtained from separateperfusions, designated PLSC-1 through PLSC-29, were assessed for theexpression of CD10, CD29, CD34, CD44, CD45, CD54, CD90, SH2 (CD105), SH3(CD73), SH4 (CD73) and HLA-1 by flow cytometry. Adherent cellsdesignated PLSC-1 to PLSC-3, PLSC-5 to PLSC-10, PLSC-15 to PLSC-21,PLSC-23, PLSC-26 and PLSC-27 were found to be positive for CD10, CD29,CD54, SH2, SH3 and SH4, and negative for CD34 and CD45. Adherent cellsdesignated PLSC-15 to PLSC-21, PLSC-23, PLSC-26 and PLSC-27 wereadditionally found to be positive for CD44, CD90 and HLA1. See Table 1,below.

mRNA was collected from adherent cells from PLSC-3 and PLCS-6 to PLSC-10cells, and rtPCR was performed using primers specific to OCT-4 (POU5F).All of the cell populations tested were positive for OCT-4 mRNA.

TABLE 1 Characterization of placental stem cells (PLSC) collected fromseparate perfusion experiments. Frozen ID # Medium (Vials) CD34 CD45CD10 CD29 CD54 SH2 SH3 SH4 SSEA4 CD44 HLA1 CD90 Oct4 PLSC-1 BW Y (2) −− + + + + + + PLSC-2 BW Y (6) − − + + + + + + PLSC-3 BW Y (2) −− + + + + + + + PLSC-4 BW None PLSC-5 BW Y (9) − − + + + + + + PLSC-6 BWY (26) − − +/low + + + + + + PLSC-7 BW Y (2) − − + + + + + + + PLSC-8 BWY (10) − + + + + + + + PLSC-9 BW Y (11) − − + + + + + + + PLSC-10 BW Y(10) − − + + + + + + + PLSC-11 D-5% FCS Y (9) PLSC-12 D-5% FCS Y (7)PLSC-13 D-5% FCS Y (5) PLSC-14 D-5% FCS Y (9) PLSC-15 Anthro-1 Y (7) −− + + + + + + + + + PLSC-16 Anthro-1 Y (8) − − + + + + + + + + + PLSC-17Anthro-1 Y (8) − − + + + + + + + + + PLSC-18 Anthro-1 Y (8) −− + + + + + + + + + PLSC-19 BWtoA Y (17) − − + + + + + + + + + PLSC-20BWtoA Y (40) − − + + + + + + + + + PLSC-21 BWtoA Y (9) − − + + + + + ++/− + + + PLSC-22 BWtoA FTE PLSC-23 Anthro-1 Y (10) −− + + + + + + + + + PLSC-24 Anthro-1 FTE PLSC-25 Anthro-1 FTE PLSC-26Anthro-1 Y (15) − − + + + + + + + + + PLSC-27 Anthro-1 Y (25) −− + + + + + + + + + +: Detected by flow cytometry, or, for OCT-4, geneexpression detected by RT-PCR. −: Not detected. Blank: Presence ofmarker was not tested. FTE: Failed to expand. BW—BioWhittaker completemedium (RPM1 1640 + 10% FBS). D-5% FCS: DMEM-5% FCS. BWtoA: BW toAnthro-1 medium

Differentiation

In separate experiments, the adherent fibroblastoid cells weredemonstrated to be stem cells. The cells were differentiated in vitrointo cells of adipocytic lineage, as evidenced by the formation of oildroplets detectable by the stain Oil Red. The cells were alsodifferentiated in vitro into cells of a neurogenic lineage as evidencedby the development of dendrite-like spindles characteristic of neuralcells, and the appearance of glial acid fibrillary protein andneurofilament proteins, both markers of neural cells. The cells werealso differentiated in vitro into cells of a chondrogenic lineage, asevidenced by the appearance of glycosaminoglycans, produced bycartilage-producing cells, that were detectable by Periodic Acid Schiffreagent. In a separate experiment, it was determined that placental stemcells did not differentiate in a NOD-SCID mouse model.

6.3 Example 3: Isolation of Placental Stem Cells from PlacentalStructures

6.3.1 Materials & Methods

6.3.1.1 Isolation of Populations of Placental Cells Comprising PlacentalStem Cells

Distinct populations of placental cells were obtained from the placentasof normal, full-term pregnancies. All donors provided full writtenconsent for the use of their placentas for research purposes. Placentalstem cells were obtained from the following sources: (1) placentalperfusate (from perfusion of the placental vasculature); and enzymaticdigestions of (2) amnion, (3) chorion, (4) amnion-chorion plate, and (5)umbilical cord. The various placental tissues were cleaned in sterilePBS (Gibco-Invitrogen Corporation, Carlsbad, Calif.) and placed onseparate sterile Petri dishes. The various tissues were minced using asterile surgical scalpel and placed into 50 mL Falcon Conical tubes. Theminced tissues were digested with IX Collagenase (Sigma-Aldrich, St.Louis, Mo.) for 20 minutes in a 37° C. water bath, centrifuged, and thendigested with 0.25% Trypsin-EDTA (Gibco-Invitrogen Corp) for 10 minutesin a 37° C. water bath. The various tissues were centrifuged afterdigestion and rinsed once with sterile PBS (Gibco-Invitrogen Corp). Thereconstituted cells were then filtered twice, once with 100 μm cellstrainers and once with 30 μm separation filters, to remove any residualextracellular matrix or cellular debris.

6.3.1.2 Cellular Viability Assessment and Cell Counts

The manual trypan blue exclusion method was employed post digestion tocalculate cell counts and assess cellular viability. Cells were mixedwith Trypan Blue Dye (Sigma-Aldrich) at a ratio of 1:1, and the cellswere read on hemacytometer.

6.3.1.3 Cell Surface Marker Characterization

Cells that were HLA ABC⁻/CD45⁻/CD34⁻/CD133⁺ were selected forcharacterization. Cells having this phenotype were identified,quantified, and characterized by two of Becton-Dickinson flowcytometers, the FACSCalibur and the FACS Aria (Becton-Dickinson, SanJose, Calif., USA). The various placental cells were stained, at a ratioof about 10 μL of antibody per 1 million cells, for 30 minutes at roomtemperature on a shaker. The following anti-human antibodies were used:Fluorescein Isothiocyanate (FITC) conjugated monoclonal antibodiesagainst HLA-G (Serotec, Raleigh, N.C.), CD10 (BD ImmunocytometrySystems, San Jose, Calif.), CD44 (BD Biosciences Pharmingen, San Jose,Calif.), and CD105 (R&D Systems Inc., Minneapolis, Minn.); Phycoerythrin(PE) conjugated monoclonal antibodies against CD44, CD200, CD117, andCD13 (BD Biosciences Pharmingen); Phycoerythrin-Cy5 (PE Cy5) conjugatedStreptavidin and monoclonal antibodies against CD117 (BD BiosciencesPharmingen); Phycoerythrin-Cy7 (PE Cy7) conjugated monoclonal antibodiesagainst CD33 and CD10 (BD Biosciences); Allophycocyanin (APC) conjugatedstreptavidin and monoclonal antibodies against CD38 (BD BiosciencesPharmingen); and Biotinylated CD90 (BD Biosciences Pharmingen). Afterincubation, the cells were rinsed once to remove unbound antibodies andwere fixed overnight with 4% paraformaldehyde (USB, Cleveland, Ohio) at4° C. The following day, the cells were rinsed twice, filtered through a30 μm separation filter, and were run on the flow cytometer(s).

Samples that were stained with anti-mouse IgG antibodies (BD BiosciencesPharmingen) were used as negative controls and were used to adjust thePhoto Multiplier Tubes (PMTs). Samples that were single stained withanti-human antibodies were used as positive controls and were used toadjust spectral overlaps/compensations.

6.3.1.4 Cell Sorting and Culture

One set of placental cells (from perfusate, amnion, or chorion), priorto any culture, was stained with 7-Amino-Actinomycin D (7AAD; BDBiosciences Pharmingen) and monoclonal antibodies specific for thephenotype of interest. The cells were stained at a ratio of 10 μL ofantibody per 1 million cells, and were incubated for 30 minutes at roomtemperature on a shaker. These cells were then positively sorted forlive cells expressing the phenotype of interest on the BD FACS Aria andplated into culture. Sorted (population of interest) and “All”(non-sorted) placental cell populations were plated for comparisons. Thecells were plated onto a fibronectin (Sigma-Aldrich) coated 96 wellplate at the cell densities listed in Table 2 (cells/cm²). The celldensity, and whether the cell type was plated in duplicate ortriplicate, was determined and governed by the number of cellsexpressing the phenotype of interest.

TABLE 2 Cell plating densities 96 Well Plate Culture Density of PlatedCells Conditions Cell Source Sorted All All Max. Density Perfusate Set#1: 40.6 K/cm² 40.6 K/cm² 93.8 K/cm² Set #2 40.6 K/cm² 40.6 K/cm² 93.8K/cm² Set #3: 40.6 K/cm² 40.6 K/cm² 93.8 K/cm² Amnion Set #1: 6.3 K/cm²6.3 K/cm² 62.5 K/cm² Set #2 6.3 K/cm² 6.3 K/cm² 62.5 K/cm² Chorion Set#1: 6.3 K/cm² 6.3 K/cm² 62.5 K/cm² Set #2 6.3 K/cm² 6.3 K/cm² 62.5 K/cm²

Complete medium (60% DMEM-LG (Gibco) and 40% MCDB-201 (Sigma); 2% fetalcalf serum (Hyclone Labs.); lx insulin-transferrin-selenium (ITS); lxlinoleic acid-bovine serum albumin (LA-BSA); 10⁻⁹ M dexamethasone(Sigma); 10⁻⁴ M ascorbic acid 2-phosphate (Sigma); epidermal growthfactor 10 ng/mL (R&D Systems); and platelet-derived growth factor(PDGF-BB) 10 ng/mL (R&D Systems)) was added to each well of the 96 wellplate and the plate was placed in a 5% CO₂/37° C. incubator. On day 7,100 μL of complete medium was added to each of the wells. The 96 wellplate was monitored for about two weeks and a final assessment of theculture was completed on day 12. This is very early in the placentalstem cell culture, and represents passage 0 cells.

6.3.1.5 Data Analysis

FACSCalibur data was analyzed in FlowJo (Tree star, Inc) using standardgating techniques. The BD FACS Aria data was analyzed using the FACSDivasoftware (Becton-Dickinson). The FACS Aria data was analyzed usingdoublet discrimination gating to minimize doublets, as well as, standardgating techniques. All results were compiled in Microsoft Excel and allvalues, herein, are represented as average±standard deviation (number,standard error of mean).

6.3.2 Results

6.3.2.1 Cellular Viability

Post-digestion viability was assessed using the manual trypan blueexclusion method (FIG. 1). The average viability of cells obtained fromthe majority of the digested tissue (from amnion, chorion oramnion-chorion plate) was around 70%. Amnion had an average viability of74.35%±10.31% (n=6, SEM=4.21), chorion had an average viability of78.18%±12.65% (n=4, SEM=6.32), amnion-chorion plate had an averageviability of 69.05%±10.80% (n=4, SEM=5.40), and umbilical cord had anaverage viability of 63.30%±20.13% (n=4, SEM=10.06). Cells fromperfusion, which did not undergo digestion, retained the highest averageviability, 89.98±6.39% (n=5, SEM=2.86).

6.3.2.2 Cell Quantification

The populations of placental cells and umbilical cord cells wereanalyzed to determine the numbers of HLA ABC⁻/CD45⁻/CD34⁻/CD133⁺ cells.From the analysis of the BD FACSCalibur data, it was observed that theamnion, perfusate, and chorion contained the greatest total number ofthese cells, 30.72±21.80 cells (n=4, SEM=10.90), 26.92±22.56 cells (n=3,SEM=13.02), and 18.39±6.44 cells (n=2, SEM=4.55) respectively (data notshown). The amnion-chorion plate and umbilical cord contained the leasttotal number of cells expressing the phenotype of interest, 4.72±4.16cells (n=3, SEM=2.40) and 3.94±2.58 cells (n=3, SEM=1.49) respectively(data not shown).

Similarly, when the percent of total cells expressing the phenotype ofinterest was analyzed, it was observed that amnion and placentalperfusate contained the highest percentages of cells expressing thisphenotype (0.0319%±0.0202% (n=4, SEM=0.0101) and 0.0269%±0.0226% (n=3,SEM=0.0130) respectively (FIG. 2). Although umbilical cord contained asmall number of cells expressing the phenotype of interest (FIG. 2), itcontained the third highest percentage of cells expressing the phenotypeof interest, 0.020±0.0226% (n=3, SEM=0.0131) (FIG. 2). The chorion andamnion-chorion plate contained the lowest percentages of cellsexpressing the phenotype of interest, 0.0184±0.0064% (n=2, SEM-0.0046)and 0.0177±0.0173% (n=3, SEM=0.010) respectively (FIG. 2).

Consistent with the results of the BD FACSCalibur analysis, the BD FACSAria data also identified amnion, perfusate, and chorion as providinghigher numbers of HLA ABC⁻/CD45⁻/CD34⁻/CD133⁺ cells than the remainingsources. The average total number of cells expressing the phenotype ofinterest among amnion, perfusate, and chorion was 126.47±55.61 cells(n=15, SEM=14.36), 81.65±34.64 cells (n=20, SEM=7.75), and 51.47±32.41cells (n=15, SEM=8.37), respectively (data not shown). Theamnion-chorion plate and umbilical cord contained the least total numberof cells expressing the phenotype of interest, 44.89±37.43 cells (n=9,SEM=12.48) and 11.00±4.03 cells (n=9, SEM=1.34) respectively (data notshown).

BD FACS Aria data revealed that the perfusate and amnion produced thehighest percentages of HLA ABC⁻/CD45/CD34⁻/CD133⁺ cells, 0.1523±0.0227%(n=15, SEM=0.0059) and 0.0929±0.0419% (n=20, SEM=0.0094) respectively(FIG. 3). The amnion-chorion plate contained the third highestpercentage of cells expressing the phenotype of interest, 0.0632±0.0333%(n=9, SEM=0.0111) (FIG. 3). The chorion and umbilical cord contained thelowest percentages of cells expressing the phenotype of interest,0.0623±0.0249% (n=15, SEM=0.0064) and 0.0457±0.0055% (n=9, SEM=0.0018)respectively (FIG. 3).

After HLA ABC⁻/CD45⁻/CD34⁻/CD133⁺ cells were identified and quantifiedfrom each cell source, its cells were further analyzed and characterizedfor their expression of cell surface markers HLA-G, CD10, CD13, CD33,CD38, CD44, CD90, CD105, CD117, CD200, and CD105.

6.3.2.3 Placental Perfusate-Derived Cells

Perfusate-derived cells appeared generally positive for HLA-G, CD33,CD117, CD10, CD44, CD200, CD90, CD38, CD105, and CD13 (FIG. 4). Theaverage expression of each marker for perfusate-derived cells was thefollowing: 37.15%±38.55% (n=4, SEM=19.28) of the cells expressed HLA-G;36.37%±21.98% (n=7, SEM=8.31) of the cells expressed CD33; 39.39%±39.91%(n=4, SEM=19.96) of the cells expressed CD117; 54.97%±33.08% (n=4,SEM=16.54) of the cells expressed CD10; 36.79%±11.42% (n=4, SEM-5.71) ofthe cells expressed CD44; 41.83%±19.42% (n=3, SEM=11.21) of the cellsexpressed CD200; 74.25%±26.74% (n=3, SEM=15.44) of the cells expressedCD90; 35.10%±23.10% (n=3, SEM=13.34) of the cells expressed CD38;22.87%±6.87% (n=3, SEM=3.97) of the cells expressed CD105; and25.49%±9.84% (n=3, SEM=5.68) of the cells expressed CD13.

6.3.2.4 Amnion-Derived Cells

Amnion-derived cells were consistently positive for HLA-G, CD33, CD117,CD10, CD44, CD200, CD90, CD38, CD105, and CD13 (FIG. 5). The averageexpression of each marker for amnion-derived was the following:57.27%±41.11% (n=3, SEM=23.73) of the cells expressed HLA-G;16.23%±15.81% (n=6, SEM=6.46) of the cells expressed CD33; 62.32%±37.89%(n=3, SEM=21.87) of the cells expressed CD117; 9.71%±13.73% (n=3,SEM=7.92) of the cells expressed CD10; 27.03%±22.65% (n=3, SEM=13.08) ofthe cells expressed CD44; 6.42%±0.88% (n=2, SEM=0.62) of the cellsexpressed CD200; 57.61%±22.10% (n=2, SEM=15.63) of the cells expressedCD90; 63.76%±4.40% (n=2, SEM=3.11) of the cells expressed CD38;20.27%±5.88% (n=2, SEM=4.16) of the cells expressed CD105; and54.37%±13.29% (n=2, SEM=9.40) of the cells expressed CD13.

6.3.2.5 Chorion-Derived Cells

Chorion-derived cells were consistently positive for HLA-G, CD117, CD10,CD44, CD200, CD90, CD38, and CD13, while the expression of CD33, andCD105 varied (FIG. 6). The average expression of each marker for chorioncells was the following: 53.25%±32.87% (n=3, SEM=18.98) of the cellsexpressed HLA-G; 15.44%±11.17% (n=6, SEM=4.56) of the cells expressedCD33; 70.76%±11.87% (n=3, SEM=6.86) of the cells expressed CD117;35.84%±25.96% (n=3, SEM=14.99) of the cells expressed CD10; 28.76%±6.09%(n=3, SEM=3.52) of the cells expressed CD44; 29.20%±9.47% (n=2,SEM=6.70) of the cells expressed CD200; 54.88%±0.17% (n=2, SEM=0.12) ofthe cells expressed CD90; 68.63%±44.37% (n=2, SEM=31.37) of the cellsexpressed CD38; 23.81%±33.67% (n=2, SEM=23.81) of the cells expressedCD105; and 53.16%±62.70% (n=2, SEM=44.34) of the cells expressed CD13.

6.3.2.6 Amnion-Chorion Plate-Derived Cells

Cells from amnion-chorion plate were consistently positive for IILA-G,CD33, CD117, CD10, CD44, CD200, CD90, CD38, CD105, and CD13 (FIG. 7).The average expression of each marker for amnion-chorion plate-derivedcells was the following: 78.52%±13.13% (n=2, SEM=9.29) of the cellsexpressed HLA-G; 38.33%±15.74% (n=5, SEM=7.04) of the cells expressedCD33; 69.56%±26.41% (n=2, SEM=18.67) of the cells expressed CD117;42.44%±53.12% (n=2, SEM=37.56) of the cells expressed CD10;32.47%±31.78% (n=2, SEM=22.47) of the cells expressed CD44; 5.56% (n=1)of the cells expressed CD200; 83.33% (n=1) of the cells expressed CD90;83.52% (n=1) of the cells expressed CD38; 7.25% (n=1) of the cellsexpressed CD105; and 81.16% (n=1) of the cells expressed CD13.

6.3.2.7 Umbilical Cord-Derived Cells

Umbilical cord-derived cells were consistently positive for HLA-G, CD33,CD90, CD38, CD105, and CD13, while the expression of CD117, CD10, CD44,and CD200 varied (FIG. 8). The average expression of each marker forumbilical cord-derived cells was the following: 62.50%±53.03% (n=2,SEM=37.50) of the cells expressed HLA-G; 25.67%±11.28% (n=5, SEM=5.04)of the cells expressed CD33; 44.45%±62.85% (n=2, SEM=44.45) of the cellsexpressed CD117; 8.33%±11.79% (n=2, SEM=8.33) of the cells expressedCD10; 21.43%±30.30% (n=2, SEM=21.43) of the cells expressed CD44; 0.0%(n=1) of the cells expressed CD200; 81.25% (n=1) of the cells expressedCD90; 64.29% (n=1) of the cells expressed CD38; 6.25% (n=1) of the cellsexpressed CD105; and 50.0% (n=1) of the cells expressed CD13.

A summary of all marker expression averages is shown in FIG. 9.

6.3.2.8 BD FACS Aria Sort Report

The three distinct populations of placental cells that expressed thegreatest percentages of HLA ABC, CD45, CD34, and CD133 (cells derivedfrom perfusate, amnion and chorion) were stained with 7AAD and theantibodies for these markers. The three populations were positivelysorted for live cells expressing the phenotype of interest. The resultsof the BD FACS Aria sort are listed in Table 3.

TABLE 3 BD FACS Aria Sort Report Events Sorted Cell Events (Phenotype %Of Source Processed of Interest) Total Perfusate 135540110 512150.037786 Amnion 7385933 4019 0.054414 Chorion 108498122 4016 0.003701

The three distinct populations of positively sorted cells (“sorted”) andtheir corresponding non-sorted cells were plated and the results of theculture were assessed on day 12 (Table 3). Sorted perfusate-derivedcells, plated at a cell density of 40,600/cm², resulted in small, round,non-adherent cells. Two out of the three sets of non-sortedperfusate-derived cells, each plated at a cell density of 40,600/cm²,resulted in mostly small, round, non-adherent cells with severaladherent cells located around the periphery of well. Non-sortedperfusate-derived cells, plated at a cell density of 93,800/cm²,resulted in mostly small, round, non-adherent cells with severaladherent cells located around the well peripheries.

Sorted amnion-derived cells, plated at a cell density of 6,300/cm²,resulted in small, round, non-adherent cells. Non-sorted amnion-derivedcells, plated at a cell density of 6,300/cm², resulted in small, round,non-adherent cells. Non-sorted amnion-derived cells plated at a celldensity of 62,500/cm² resulted in small, round, non-adherent cells.

Sorted chorion-derived cells, plated at a cell density of 6,300/cm²,resulted in small, round, non-adherent cells. Non-sorted chorion-derivedcells, plated at a cell density of 6,300/cm², resulted in small, round,non-adherent cells. Non-sorted chorion-derived cells plated at a celldensity of 62,500/cm², resulted in small, round, non-adherent cells.

A majority of the above non-adherent cells, when cultured, adhered tothe tissue culture surface and assumed a fibroblastoid shape.

Subsequent to the performance of the experiments related above, andfurther culture of the placental stem cells, it was determined that thelabeling of the antibodies for CD117 and CD133, in which astreptavidin-conjugated antibody was labeled with biotin-conjugatedphycoerythrin (PE), produced background significant enough to resemble apositive reading. This background had initially resulted in theplacental stem cells being deemed to be positive for both markers. Whena different label, APC or PerCP was used, the background was reduced,and the placental stem cells were correctly determined to be negativefor both CD117 and CD133.

6.4 Example 4: Characterization of Placental Stem Cell Marker Expression

This example describes experiments designed to further characterizeexpression of a variety of protein expression markers by placental stemcells as follows: CD200⁺, CD105⁺, CD90⁺, CD10⁺, cytokeratin 18⁺, CD34⁻,and CD45⁻. In addition, the baseline expression of hepatocyte markers onuninduced placental stem cells is assessed, including, for example,expression of cytokeratin 18, secretion of hepatocyte growth factor(HGF) and expression of asialoglycoprotein receptor.

Placental stem cell marker expression is assessed according to thefollowing exemplary flow cytometry protocol. Placental stem cells arefirst trypsinized, then incubated with fluorochrome-conjugatedantibodies on ice for 30 minutes in the dark, rinsed twice with coldPBS-2% BSA and then analyzed with a FACSCalibur (BD Biosciences).Exemplary antibodies suitable for these assays are PerCP-conjugatedanti-CD34, FITC conjugated anti-CD105, APC-conjugated anti-CD10, and PEconjugated CD200. Other suitable antibody reagents include, theappropriate fluorophore combinations: APC-conjugated anti-HLA-ABC,PE-conjugated anti-CD31, PerCP-conjugated anti-CD45, FITC-conjugatedanti-CD38, PE-conjugated anti-CD44, FITC-conjugated anti-cytokeratin K(or cytokeratin 18), APC-conjugated anti-CD90, APC-conjugated anti-CD86,FITC-conjugated anti-CD80, FITC-conjugated anti-HLA DR,DQ,DP,PE-conjugated anti-3-2-microglobulin, APC-conjugated anti-CD133 andPerCP-conjugated anti-CD117. Except where otherwise noted, theseantibodies are available from BD-Pharmingen. Analysis and statistics offlow cytometry data is accomplished with Flowjo (Tree Star, Inc.Ashland, Oreg.).

Cytokines produced by placental stem cells are analyzed by collectingsupernatants of cultured cells using a LincoPlex Adipogenic analysis kitand a Luminex instrument according to the manufacturer's instructions.

6.5 Example 5: Induction of Placental Cell Differentiation intoHepatocytes Using Sodium Butyrate

This example describes exemplary methods for induction of hepatocytedifferentiation of placental stem cells using sodium butyrate. Themethods are designed to characterize Na-butyrate induced placental stemcells using a variety of protein expression markers, expression ofhepatocyte specific genes and hepatocyte specific markers such ascytokeratin 18 (a molecule already expressed in undifferentiatedplacental stem cells) and asialoglycoprotein receptor. The ability ofinduced placental stem cells to produce intracellular albumin andsecretion of urea is assessed.

To induce differentiation, placental stem cells are plated at a densityof about 10⁵ cells/well in 0.1% gelatin coated six well plates inIscove's Modified Dulbecco's medium (IMDM) (Gibco, Cat #31980-030)containing 20% fetal bovine serum (Gibco), 4 mM L-glutamine (Gibco), 100U/ml penicillin, 100 U/ml streptomycin (Gibco) and 10 μg/ml gentamicin(Gibco). Gelatin solution (0.1%) is prepared by dissolving 0.5 μm ofporcine gelatin (Sigma-Aldrich, Cat # G-2500) in 500 ml of PhosphateBuffered Saline (PBS) (Gibco, Cat #20012-027) with gentle heating. Tocoat plates with gelatin, 2 ml of 0.1% gelatin solution is added to eachwell of a polystyrene tissue culture treated plate. The plates areincubated for 2 hrs following which the gelatin solution is aspirated.The plates are washed once with PBS and then 2.5 ml of IMDM is addedfollowed by about 10⁵ cells/well. Optionally, cells are exposed to 1%DMSO (Sigma-Aldrich) for the next 4 days followed by exposure toNa-butyrate (Sigma Aldrich, Cat # B5887) at different concentrations (1,2.5, 5.10 mM) for 6 days. Media is replaced daily.

In order to measure function of the differentiated cell, a secondaryculture is initiated where cells are removed from the primary culturedish and replated on collagen type I coated (BD Biosciences) andpolystyrene 12 well plates at a density of about 10⁵ cells/well. Mediais changed 24 hrs after replating and cells are tested for functionalassays 48 hrs after replating.

6.6 Example 6: Aggregation of Placental Stem Cells byAlginate-Poly-L-Lysine Microencapsulation in Preparation forDifferentiation into Hepatocytes

This example describes exemplary methods for aggregating placental stemcells using alginate microencapsulation technology in preparation fordifferentiating the cells into hepatocytes.

Alginate Poly-L-Lysine Encapsulation

An alginate solution is generated by dissolving 2.2 g of alginate(Sigma-Aldrich, MW: 100,000-200,000 g/mol, G-Content: 65%-70%) in 100 mLof Ca²⁺ free DMEM (Gibco), using a heated magnetic stir plate at atemperature of 45° C. The solution is then filtered using a 25-micronsyringe filter (Fisher Brand, Pittsburgh, Pa.). A confluent monolayer ofadherent cells is removed following trypsin incubation, centrifuged for10 minutes at 1200 rpm, and resuspended in PBS. The cells are washedtwice more with PBS (Gibco), resuspended in 2 mL of their respectivemedia and both cell number and viability assessed using the method oftrypan blue (Gibco) exclusion. To create the cell-alginate mixture a 1mL aliquot of cell suspension with a seeding density of about 5×10⁷cells/ml is added to 9 mL of a 2.2% (w/v) alginate solution to yield afinal cell seeding density of about 5×10⁶ cells/ml and a final alginateconcentration of 2.0% (w/v). This solution is transferred to a 10 mlsyringe (BD Biosciences), which, in turn, is connected to a syringe pump(KD Scientific, Holliston, Mass.). Alginate beads are generated using anelectrostatic bead generator (Nisco, ZUrich, Switzerland) at a flow rateof 40 ml/hour, and an applied voltage of 6.5 kV, resulting in beads witha diameter of 500 μm. The beads are extruded into a 200 mL bath of CaCl₂(100 mM) (Sigma-Aldrich), containing 145 mM NaCl (Sigma-Aldrich), and 10mM MOPS (Sigma-Aldrich) and are left to polymerize for 10 minutes atroom temperature. Beads are transferred to a tissue culture treated T-25flask (Falcon, BD Biosciences), following the polymerization step. TheCaCl₂ solution is removed using a 5 mL pipette, and the beads are washedwith 5 mL HEPES (Gibco). The buffer is removed and the beads areresuspended in 5 ml of poly-L-lysine (PLL) (Sigma-Aldrich, MW: 68,600g/mol) (0.05% w/v) for 2 minutes. The PLL is then gently removed,replaced with HEPES to wash the beads and the beads are ultimatelyresuspended into 5 ml of cell culture media. Media is changed at, e.g.,4, 8, 11, 14 and 17 days post-encapsulation.

Assessment of Intracapsular Viability

Viability within beads is assessed with a calcein (Molecular Probes,Eugene, Oreg.), ethidium homodimer (Molecular Probes) stain immediatelyfollowing encapsulation. Calcein is only cleaved to form fluorescentproducts in live cells while ethidium homodimer is only incorporatedinto the nucleus of dead cells. Calcein and ethidium homodimer imagesare acquired using a Zeiss Axiovert LSM laser scanning confocalmicroscope (Germany) fitted with a 495 nm excitation filter and emissionfilters of 515 nm and 635 nm, respectively. Specifically, z-sections of500 um diameter beads are taken at 10 um intervals, for a total depth of250 um. Three experiments incorporated an analysis of 15 beads perexperiment. Digitized images are quantified using Olympus MICROSUITE™.Viability is assessed for each cross-section of every bead.

Cell Recovery and Assessment Following Depolymerization

Functional analysis and aggregate size calculations are performed oneach of the analysis days following the release of cells from the beads.A minimum of 1500 beads is analyzed per replicate per condition. Beadsare washed with PBS, and 100 mM sodium citrate (Fisher Scientific),containing 10 mM MOPS (Sigma-Aldrich) and 27 mM NaCl (Sigma-Aldrich) areadded for 30 minutes at 37° C. to induce depolymerization. To determinerecovery yield following depolymerization, a known concentration ofcells is encapsulated and immediately depolymerized. Followingcentrifugation, both the cell pellet as well as the supernatant (whichcontains bead particles but no intact beads) are counted using trypanblue exclusion (which does not stain the capsule), and after a massbalance, verify that approximately the same number of cells are presentas in the starting population. This method demonstrates a 98% recoveryof the encapsulated cell population. The released cells are centrifugedat 1200 rpm for 10 minutes, the sodium citrate solution aspirated, thecell pellet washed with PBS (3×), and resuspended in cell specificmedia. The cells are then counted using the trypan blue method describedabove.

Intracapsular Aggregate Size Determination

103271 Beads are sampled from tissue culture treated T-25 flasks andtransferred to 35 mm Mattek dishes (Mattek, Ashland, Mass.) immediatelyfollowing encapsulation (day 0), and on the analysis days 8, 11, 14, 1720. Bright field images are acquired using a Zeiss Axiovert LSM laserscanning confocal microscope (Germany). Specifically, z-sections of 500um diameter beads are taken at 50 um intervals, to avoid multiplequantification of the same aggregate, for a total depth of 250 um.Images are quantified using Olympus Microsuite. In short, a colorthreshold is first applied in order to distinguish cellular aggregatesfrom the image background. The diameter of the aggregate is thendetermined using the mean diameter particle measurement.

6.7 Example 7: In Situ Indirect Immunofluorescent Cytokeratin-18 andIntracellular Albumin Analysis

This example describes exemplary methods for assessing cytokeratin-18and albumin expression by hepatocytes obtained from differentiatedplacental stem cells. Differentiated cells (recovered followingdepolymerization if appropriate) are transferred to a tissue culturetreated 24 well plate (Falcon, BD Biosciences). Specifically, theisolated cell population is diluted to about 6×10⁴ cells in 0.75 ml ofmedia and incubated for one hour at 37° C. to allow for cell attachment.The cells are then washed for 10 min in cold PBS and fixed in 4%paraformaldehyde (Sigma-Aldrich) in PBS for 15 minutes at roomtemperature. The cells are washed twice for 10 min in cold PBS and thentwice for 10 min in cold saponine/PBS (SAP) membrane permeabilizationbuffer containing 1% bovine serum albumin (BSA) (Sigma-Aldrich), 0.5%saponine (Sigma-Aldrich) and 0.1% sodium azide (Sigma-Aldrich). Todetect intracellular albumin, the cells are subsequently incubated for30 minutes at 4° C. in a SAP solution containing rabbit anti-mousealbumin antibody (150 μg/ml) (MP Biomedicals, Irvine, Calif.), or normalrabbit serum (150 μg/ml) (MP Biomedicals) as an isotype control, washedtwice for 10 min in cold SAP buffer, and then treated for 30 minutes at4° C. with the secondary antibody, FITC-conjugated donkey anti-rabbit,diluted 1:500 (Jackson Immuno Labs, Westgrove, Pa.). To detectcytokeratin 18, cells are incubated for 30 minutes at 4° C. in a SAPsolution containing rabbit anti-mouse cytokeratin 18 antibody (IgG1)(1:50 dilution) (Santa Cruz Biotechnology) or the IgG1 fraction ofnormal rabbit serum (1:100 dilution) (Santa Cruz Biotechnology) as anisotype control, and then treated for 30 minutes at 4° C. with thesecondary antibody, FITC-conjugated goat anti-rabbit, diluted 1:200(Jackson Immuno Labs, Westgrove, Pa.). For both stains, cells are thenwashed once with cold SAP buffer and once with cold PBS. Fluorescentimages are acquired using a computer-interfaced inverted Olympus IX70microscope. Specimens are excited using a 515 nm filter. Fluorescentintensity values are determined for each cell using Olympus MICROSUITE™.Experimental intensity values for each cell are calculated aftersubtracting the average intensity of the isotype control.

6.8 Example 8: Glycogen Staining

This example describes exemplary methods for assessing glycogenproduction by hepatocytes obtained from differentiated placental stemcells. Following depolymerization, cells are transferred to tissueculture treated 24 well plates (Falcon, BD Biosciences) and fixed with10% formalin-ethanol fixative solution for 15 minutes at roomtemperature, with subsequent washes with PBS. Fixed cells are exposed to0.25 ml of Periodic Acid Solution (Sigma Aldrich) per well for 5 minutesat room temperature. Glycols are oxidized to aldehydes in this process.After washing cells with PBS to remove the PAS, 1 ml of Schiff's reagentis added per well and cells exposed for 15 minutes at room temperature.Schiff's reagent, a mixture of pararosaniline and sodium metabisulfite,reacts to release a pararosaniline product that stains theglycol-containing cellular elements. A third PBS wash to remove thereagent is followed by image acquisition with an Olympus IX70 microscopeand Olympus digital camera.

6.9 Example 9: Glucose and Lactate Measurements

This example describes exemplary methods for assessing glucose andlactate consumption and/or production by hepatocytes obtained fromdifferentiated placental stem cells. Supernatants (1 ml) were collectedin triplicate for each cell type in secondary culture and then testedusing a Bioprofile Bioanalyzer 400 (Nova Biomedical, Waltham, Mass.) formetabolite measurements of glucose and lactate. On each day of analysis,base media glucose and lactate measurements were measured and the meanvalues were subtracted from the test values to obtain uptake orproduction. Cells were counted for each condition to get the finalconsumption or production rate.

6.10 Example 10: Urea Analysis

This example describes exemplary methods for assessing urea productionby hepatocytes obtained from differentiated placental stem cells. Mediasamples are collected directly from cell cultures and stored at −20° C.for subsequent urea content analysis. Urea synthesis is assayed using acommercially available kit (StanBio, Boerne, Tex.). A standard curve isgenerated by creating serial dilutions of a urea standard from 300 μg/mlto 0 μg/ml. Absorbance readings are obtained using a Biorad (Hercules,Calif.) Model 680 plate reader with a 585n emission filter. Urea valuesare normalized to the cell number recorded on the day of media samplecollection.

6.11 Example 11: Sandwich ELISA for Detection of Albumin Secretion

This example describes exemplary methods for assessing albumin secretionby hepatocytes obtained from differentiated placental stem cells. Inorder to detect secreted albumin within the media supernatants obtainedon each of the analysis days, a commercially available mouse albuminELISA kit (Bethyl Laboratories, # E90-134) is used. A standard curve isgenerated by creating serial dilutions of an albumin standard from 7.8to 10,000 ng/mL. Absorbance readings are obtained using a Biorad(Hercules, Calif.) Model 680 plate reader with a 450 nm emission filter.Albumin values are normalized to the cell number recorded on the day ofmedia sample collection.

6.12 Example 12: Mouse Model of Hepatitis B Infection

This Example describes a mouse model of hepatitis B virus (HBV)infection that uses hepatocytes differentiated from the placental stemcells described elsewhere herein. The mouse is produced by (1)irradiating a mouse, which is then protected by administration of SCIDmouse bone marrow; and (2) administration of HBV-infected hepatocytesthat have been differentiated from placental stem cells. The mouse isthen administered a compound that is to be tested for its ability toreduce viral replication or viral load.

Placental Stem Cells.

Adherent placental stem cells are obtained by one or more of the methodsdescribed in Example 1, above.

Preparation of Hepatocytes.

Placental stem cells are differentiated according to the methoddescribed in Examples 4, above.

HBV Infection of Placental Stem Cell-Derived Hepatocytes.

Placental stem cell-derived hepatocytes in alginate are collected bycentrifugation and resuspended in 1 mL of high-titer HBV DNA human serumsupplemented with 3 μg hexidementhrine bromide (Sigma-Aldrich, H-9268,St. Louis, Mo.) and 0.5 μg human interleukin 6 (IL-6; Preprotech,London, England).

Preparation of Mice.

CB16F or BNX (beige/nude/xid) mice, and NOD/SCID mice at age 6-10 weeks,are used. Mice are fed sterile food and acid water containingciprofloxacin (20 μg/mL). CB16F mice (Harlan Laboratories, WeitzmannInstitute Animal Breeding Center, Rehovot, Israel) are exposed to totalbody irradiation at a dose of about 4 Gy followed three days later by adoes of about 11 Gy from a gamma beam 150-A ⁶⁰Co source (Atomic Energyof Canada, Kanata, Ontario, Canada) at an irradiation rate of about 0.7Gy/min. From about 4×10⁶ to about 6×10⁶ bone marrow cells from NOD/SCIDmice, in 0.2 mL phosphate-buffered saline, are immediately transplantedinto the irradiated mice. Bone marrow cells are prepared by disruptionof femoral and tibial bones in an Omni-Mixer in phosphate bufferedsaline to obtain marrow cells, followed by depletion of T cells from theresulting cell suspension. See Levite et al., Transplantation 8:1-3(1991). The mice are injected daily with 1 mg Fortum (Glaxo)intraperitoneally for 5 days following bone marrow transplantation.Directly after bone marrow cell transplantation, HBV-infected placentalstem cell-derived hepatocytes (about 5×10⁷) are then transplanted intothe irradiated mice under the kidney capsule or into the ear pinna.Engraftment of hepatocytes can be assessed by biopsy andhematoxylin-eosin staining, and by detection of expression of humanserum albumin-encoding mRNA in the transplanted tissue.

BNX mice are prepared as CB16F mice, except that BNX mice are irradiatedonce at a dose of 11 Gy, and transplantation of the HBV-infectedhepatocytes takes place at least 10 days after bone marrow celltransplantation.

Extraction of DNA From HBV-Injected Sera.

DNA is extracted from 100 μL of serum by proteinase K digestion in 400μL reaction mixture containing 0.25% sodium dodecyl sulfate, 5 mmol/LEDTA, 10 mmol/L Tris HCl (pH 8.0), and 250 μg/mL proteinase K (Sigma,St. Louis, Mo.). After 2.5 hours at 65° C., 1 μg of a DNA carrier and0.5 mg BSA is added. DNA is then extracted by phenol-chloroform andprecipitated in ethanol overnight at −20° C. Following centrifugationfor 15 minutes at 20,000 g, the DNA pellets is washed with 70% ethanol,dried, and resuspended in 50 μL of water.

Determination of HBV DNA Level in Mouse Sera.

The HBV DNA copy number is determined by semiquantitative PCR usingHBV-specific primers. PCR products are separated on a standard 2%agarose gel. 50 μL of the products are dot blotted and hybridizedovernight at 42° C. with an appropriate [³²P]-labeled DNA fragment(Rediprime DNA labeling system, Amersham, Buckinghamshire, UK). The blotis then washed in 0.1×0.15 mol/L NaCl and 0.015 mol/L sodium citrate, pH7.0 and 1% SDS at 55° C., and exposed to X ray film. The intensity ofdots is read on an ELISA reader, e.g., Dynatech at 630 nm, or on aMolecular Dynamics computing densitometer Model 300A. Viral load isdetermined using a standard curve composed of DNA samples obtained fromcalibrated human serum diluted in normal mouse serum comprising copynumbers from 10² to 10⁷ per 100 μL samples. A mouse having a viral loadof less than about 5×10³/mL serum is considered to be uninfected.Primers used in this procedure recognize both covalently closed circularand relaxed forms of HBV.

HBV viral load can, alternately or additionally, be determined by ELISAusing one or more antibodies that recognize a surface antigen of HBV.

Determination of HBV Covalently Closed Circular DNA in EngraftedHepatocytes.

This step can be performed if confirmation of viral replication isneeded. DNA is extracted from hepatocytes collected by centrifugation(about 1×10⁵) and resuspended in 100 μL of H₂O. Fifty μL is subjected toPCR using HBV-specific primers in 100 μL reaction mixture containing 13Taq Pol buffer, 2.5 mmol/L MgCl₂, 0.2 mmol/L of each dNTP, 50 pmol ofeach primer, 1 mg/mL BSA, and 2.5 U of Taq Pol. (Promega). The PCRreaction is programmed for 2 minutes at 94° C., and then 30 cycles, 1minute at

94° C., and 3 minutes at 72° C., with a final elongation reaction of 5minutes at 72° C. PCR products are analyzed on a 2% agarose gel and bydot-blot hybridization using a DNA fragment corresponding to a portionof the core sequence. This procedure uses primers that recognize onlythe covalently closed circular form of HBV.

Determination of Antiviral Activity of Compounds.

Once viremia is established, the mice are administered a compound thatis to be tested for anti-HBV activity. The route of administration isdetermined on a compound-by-compound basis, but is generally eitherintraperitoneal or intravenous. Administration of the compound isperformed at 6-17 days post-transplantation with infected hepatocytes.On days 2 and 9 post-administration, serum is drawn from the mice andassessed for viral load using antibody to HBsAg (HBV surface antigen)and PCR to detect HBV covalently closed circular DNA (cccHBV). Thecompound is determined to be an antiviral compound if the viral load isdetectably reduced (e.g., statistically significantly reduced) comparedto the viral load in mice not administered the compound. Viral load canbe compared to the amount of cccHBV present to determine whether acompound that reduces viral load is an inhibitor of HBV replication.

6.13 Example 13: Induction of Differentiation of Placental Stem Cellsinto Chondrocytes

6.13.1 General Method

Chondrogenic differentiation of placental stem cells is generallyaccomplished as follows:

1. Placental stem cells are maintained in MSCGM (Cambrex) or DMEMsupplemented with 15% cord blood serum.

2. Placental stem cells are aliquoted into a sterile polypropylene tube.The cells are centrifuged (150×g for 5 minutes), and washed twice inIncomplete Chondrogenesis Medium (Cambrex).

3. After the last wash, the cells are resuspended in CompleteChondrogenesis Medium (Cambrex) containing 0.01 μg/ml TGF-beta-3 at aconcentration of 5×10(5) cells/ml.

4. 0.5 ml of cells is aliquoted into a 15 ml polypropylene culture tube.The cells are pelleted at 150×g for 5 minutes. The pellet is left intactin the medium.

5. Loosely capped tubes are incubated at 37° C., 5% CO2 for 24 hours.

6. The cell pellets are fed every 2-3 days with freshly preparedcomplete chondrogenesis medium.

7. Pellets are maintained suspended in medium by daily agitation using alow speed vortex.

8. Chondrogenic cell pellets are harvested after 14-28 days in culture.

9. Chondrogenesis is characterized by e.g., observation of production ofesoinophilic ground substance, assessing cell morphology, an/or RT/PCRconfirmation of collagen 2 and/or collagen 9 gene expression and/or theproduction of cartilage matrix acid mucopolysaccharides, as confirmed byAlcian blue cytochemical staining.

Chondrogenesis can also be assessed by gene expression for early stagechondrogenesis markers fibromodulin and cartilage oligomeric matrixprotein; gene expression for mid-stage chondrogenesis markers aggrecan,versican, decorin and biglycan; and gene expression for types II and Xcollagens and chondroadherein, markers of mature chondrocytes.

Placental stem cells can also be induced to chondrogenesis by the methodabove, wherein the placental stem cells are cultured on nanofibrousscaffolds such as poly(L-lactic acid) (PLLA), type I collagen, or acopolymer of vinylidene fluoride and trifluoroethylene (PVDF-TrFE),beginning at step 3, without centrifugation step 4.

6.13.2 Differentiation of Placental and Umbilical Cord Stem Cells intoChondrogenic Cells

This Example demonstrates the differentiation of placental stem cellsinto chondrogenic cells and the development of cartilage-like tissuefrom such cells.

Cartilage is an avascular, alymphatic tissue that lacks a nerve supply.Cartilage has a low chondrocyte density (<5%), however these cells aresurprisingly efficient at maintaining the extracellular matrix aroundthem. Three main types of cartilage exist in the body: (1) articularcartilage, which facilitates joint lubrication in joints; (2)fibrocartilage, which provides shock absorption in, e.g., meniscus andintervertebral disc; and (3) elastic cartilage, which providesanatomical structure in, e.g., nose and ears. All three types ofcartilage are similar in biochemical structure.

Joint pain is a major cause of disability and provides an unmet need ofrelief in the area of orthopedics. Primary osteoarthritis (which cancause joint degeneration), and trauma are two common causes of pain.Approximately 9% of the U.S. population has osteoarthritis of hip orknee, and more than 2 million knee surgeries are performed yearly.Unfortunately, current treatments are more geared towards treatment ofsymptoms rather than repairing the cartilage. Natural repair occurs whenfibroblast-like cells invade the area and fill it with fibrous tissuewhich is neither as resilient or elastic as the normal tissue, hencecausing more damage. Treatment options historically included tissuegrafts, subchondral drilling, or total joint replacement. More recenttreatments however include CARTICEL®, an autologous chondrocyteinjection; SYNVISC® and ORTHOVISC®, which are hyaluronic acid injectionsfor temporary pain relief; and CHONDROGEN™, an injection of adultmesenchymal stem cells for meniscus repair. In general, the trend seemsto be lying more towards cellular therapies and/or tissue engineeredproducts involving chondrocytes or stem cells.

Materials and Methods.

Two placental stem cell lines from amnion/chorion, designated AC61665,P3 (passage 3) and AC63919, P5, and two from umbilical cord, designatedUC67249, P2 and UC67477, P3 were used in the studies outlined below.Human mesenchymal stem cells (MSC) were used as positive controls, andan osteosarcoma cell line, MC3T3, and human dermal fibroblasts (HDF)were used as negative controls.

Placental and umbilical cord stem cells were isolated and purified fromfull term human placenta by enzymatic digestion. Human MSC cells and HDFcells were purchased from Cambrex, and MC3T3 cells were purchased fromAmerican Type Culture Collection. All cell lines used were centrifugedinto pellets in polypropylene centrifuge tubes at 800 RPM for 5 minutesand grown in both chondrogenic induction media (Cambrex) andnon-inducing basal MSC media (Cambrex). Pellets were harvested andhistologically analyzed at 7, 14, 21 and 28 days by staining forglycosaminoglycans (GAGs) with Alcian Blue, and/or for collagens withSirius Red. Collagen type was further assessed with immunostaining. RNAanalysis for cartilage-specific genes was performed at 7 and 14 days.

Results

Experiment 1: Chondrogenesis studies were designed to achieve three mainobjectives: (1) to demonstrate that placental and umbilical cord stemcells can differentiate and form cartilage tissue; (2) to demonstratethat placental and umbilical cord stem cells can differentiatefunctionally into chondrocytes; and (3) to validate results obtainedwith the stem cells by evaluating control cell lines.

For objective 1, in a preliminary study, one placental stem cell linewas cultured in chondrogenic induction medium in the form of cellpellets, either with or without bone morphogenic protein (BMP) at afinal concentration of 500 ng/mL. Pellets were assessed for evidence ofchondrogenic induction every week for 4 weeks. Results indicated thatthe pellets do increase in size over time. However, no visualdifferences were noted between the BMP⁺ and BMP⁻ samples. Pellets werealso histologically analyzed for GAGs, an indicator of cartilage tissue,by staining with Alcian Blue. BMP⁺ cells generally appeared moremetabolically active with pale vacuoles whereas BMP cells were smallerwith dense-stained nuclei and less cytoplasm (reflects low metabolicactivity). At 7 days, BMP+ cells had stained heavily blue, while BMP⁻had stained only faintly. By 28 days of induction, both BMP+ and BMP⁻cells were roughly equivalently stained with Alcian Blue. Overall, celldensity decreased over time, and matrix overtook the pellet. Incontrast, the MC3T3 negative cell line did not demonstrate any presenceof GAG when stained with Alcian Blue.

Experiment 2: Based on the results of Experiment 1, a more detailedstudy was designed to assess the chondrogenic differentiation potentialof two placental stem cell and two umbilical cord stem cell lines. Inaddition to the Alcian Blue histology, cells were also stained withSirius Red, which is specific for type II collagen. Multiple pelletswere made for each cell line, with and without induction media.

The pelleted, cultured cell lines were first assessed by grossobservation for macroscopic generation of cartilage. Overall, the steincell lines were observed to make pellets as early as day 1. Thesepellets grew over time and formed a tough matrix, appearing white,shining and cartilage-like, and became mechanically tough. By visualinspection, pellets from placental stem cells or umbilical cord stemcells were much larger than the MSC controls. Control pellets innon-induction media started to fall apart by Day 11, and were muchsmaller at 28 days than pellets developed by cells cultured inchondrogenic induction medium. Visually, there were no differencesbetween pellets formed by placental stem cells or umbilical cord.However, the UC67249 stem cell line, which was initiated indexamethasone-free media, formed larger pellets. Negative control MC3T3cells did not form pellets; however, HDFs did form pellets.

Representative pellets from all test groups were then subjected tohistological analysis for GAG's and collagen. Generally, pellets formedby the stem cells under inducing conditions were much larger and stayedintact better than pellets formed under non-inducing conditions. Pelletsformed under inducing conditions showed production of GAGs andincreasing collagen content over time, and as early as seven days, whilepellets formed under non-inducing conditions showed little to nocollagen production, as evidenced by weak Alcian Blue staining. Ingeneral, the placental stem cells and umbilical cord stem cellsappeared, by visual inspection, to produce tougher, larger pellets, andappeared to be producing more collagen over time, than the mesenchymalstem cells. Moreover, over the course of the study, the collagenappeared to thicken, and the collagen type appeared to change, asevidenced by changes in the fiber colors under polarized light (colorscorrelate to fiber thickness which may be indicative of collagen type).Non-induced placental stem cells produced much less type II collagen, ifany, compared to the induced stem cells. Over the 28-day period, celldensity decreased as matrix production increased, a characteristic ofcartilage tissue.

These studies confirm that placental and umbilical cord stem cells canbe differentiated along a chondrogenic pathway, and can easily beinduced to form cartilage tissue. Initial observations indicate thatsuch stem cells are preferable to MSCs for the formation of cartilagetissue.

6.14 Example 14: Induction of Differentiation into Chondrocytes byNanofibrous Scaffolds

This example describes methods for inducing the differentiation of stemcells, including placental stem cells or mesenchymal stem cells frombone marrow (BM-MSC), into chondrocytes with nanofibrous scaffolds. Theobjectives of this example are threefold: 1) to characterizechondrogenic differentiation of placental stem cells in vitro; 2)determine the optimum scaffold for stimulating chondrogenicdifferentiation of placental stem cells in vitro; and 3) evaluate invivo repair of osteochondral defects in a rabbit model using placentalstem cells-scaffold constructs.

To accomplish Objective 1, dynamic pellet placental stem cells culturesare used to lengthen culture duration beyond 28 days. Temporal geneexpression as well as biochemical and histological analyses of early andlate stage markers of chondrogenesis for placental stem cells in staticas well as dynamic pellet cultures are assessed. Placental stem cellsare cultured with or without TGF-β₃ in pellet cultures under static ordynamic conditions for up to 56 days. By real-time PCR, quantitativegene expression is performed for early stage markers of fibromodulin andcartilage oligomeric matrix protein. Mid-stage markers of aggrecan,versican, decorin and biglycan are also assessed. Genes for types II andX collagens and chondroadherin, which are characteristic of maturechondrocytes, are also assessed. Biochemical assays are performed fortype IT collagen, glycosaminoglycan, and proteoglycan synthesis. Tissuemorphology of the chondrogenic pellets are also characterized byhistological staining during the time course.

To accomplish Objective 2, the ability of electrospun nanofibrousscaffolds to promote placental stem cell differentiation intochondrocytes is assessed. Scaffolds composed of poly(L-lactic acid)(PLLA), type I collagen and a copolymer of vinylidene fluoride andtrifluoroethylene (PVDF-TrFE) are assessed. Placental stem cells areloaded onto scaffolds generated from these materials and cultured inboth static and dynamic conditions. Quantitative gene expression,biochemical and histological analyses, and mechanical testing areperformed during the study time course.

To accomplish Objective 3, chondral repair by placental stem cells isassessed by in vivo functional evaluation in an animal model that willnot spontaneously heal a cartilage defect such as, for example, a rabbitosteochondral defect model. Scaffolds that support chondrogenicdifferentiation are evaluated in this model in combination withplacental stem cells. Repair is evaluated by histochemical staining,specifically accessing the extent of cartilage union between uninjuredcartilage and repaired cartilage. Osteo-chondral repair is also measuredby mechanical evaluation of samples excised from the site of theoriginal defect.

6.14.1 Fibrous Scaffold Fabrication

This example describes fabrication and characterization of exemplarynanofiber non-woven meshes. The technique of electrospinning wasemployed to produce nanoscale fiber meshes. The resulting meshes havehigh surface area, controllable porosity, architecture and mechanicalproperties. Fibers produced with this technique are on the same scale asthe fibers of the ECM. poly(L-lactic acid) (PLLA) and poly lacticglycolic acid (PLGA) were used as the polymer compositions since theyare one of the most widely used biomaterials in the tissue engineeringfield. The potential use of these scaffolds as tissue engineeringscaffolds was then assessed by cell proliferation and differentiation ofhuman MSCs.

The electrospinning process is affected by varying the electricpotential, flow rate, solution concentration, capillary-collectordistance, diameter of the needle, and ambient parameters, e.g.,temperature. To fabricate PLLA and PLGA scaffolds of four distinct fiberdiameters, namely 290 nm, 1 μm, 5 μm and 9 μm, the voltage [20 KV] andcollector to needle distance [30 cm] were kept constant. The needlegauge size [12 G; 22 G], the flow rate [0.05-0.1 mL/min] and thesolution concentration [10-25 w/w %] were varied.

The average diameter distribution of PLLA and PLGA electrospun matsgenerated thereby is listed in Table 4. Microfiber and the nanofiberscaffolds of both PLLA and PLGA had a porosity of 39% and 47%,respectively. The morphology of the electrospun fibers was observed byscanning electron microscopy. By inspection, the fibers were free ofbeads, appeared round and were aligned randomly in a non-woven fashion.

TABLE 4 Polymer Average Diameter Polymer Average Diameter PLLA-1 290 ±84 nm PLGA-1 380 ± 0.80 nm PLLA-2 1 ± 0.4 μm PLGA-2 1 ± 0.3 μm PLLA-3 5± 1.5 μm PLGA-3 6 ± 1.5 μm PLLA-4 9 ± 2.0 μm PLGA-4 9 ± 1.6 μm

6.14.2 Seeding of Human MSCs on Nanofibrous Scaffolds

Human BM-MSCs isolated from whole bone marrow and subcultured wereseeded onto microfiber and nanofiber scaffolds. Cell culture plastic wasused as a control surface. BM-MSCs grown on both nano and microfiberscaffolds had similar growth kinetics. Cell morphology and uniformity ofthe cell layer was observed by SEM. Cells seeded on nanofibers wereuniformly distributed across the scaffold surface whereas cells onmicrofiber scaffolds were spread out along the fibrils and lessuniformly distributed, regardless of composition. This finding was alsoconfirmed using actin cytoskeleton staining and viewed by confocalmicroscopy.

Chondrogenic differentiation of BM-MSCs in static tissue cultureconditions also demonstrated an expression of Type II collagen for cellsseeded on nanofiber scaffolds without the presence of inductive factorsin the media. Thus, these findings suggest that nanofiber architecturespromote chondrogenic differentiation, even without the presence ofinductive factors in the culture media.

6.14.3 In Vitro Chondrogenic Differentiation of Placental Stem Cells

To examine the chondrogenic potential of placental stem cells isolatedand expanded under typical conditions, placental stem cells were grownin pellet culture in the presence of chondrogenic induction media. Theduration of static cell culture experiments was limited to 28 days dueto decreased cell content of pellets. Histological sections were takento examine the pellets for functional differentiation and the presenceof glycosaminoglycans (GAGs) and collagen. Quantitative protein and geneexpression analyses were used to further characterize the pellets.Immune markers on differentiated placental stem cells were compared toundifferentiated placental stem cells, which are known to beimmunosuppressive.

From the histological sections, it was determined that placental stemcells formed tighter pellets than BM-MSCs. Both placental stem cells andBM-MSCs stained for GAGs and collagen, while a control cell line (humandermal fibroblasts, HDF) formed loosely organized pellets with no GAGsand little collagen expression.

Protein and gene expression were used to quantify chondrogenesis byELISA and RT-PCR, respectively. ELISA data confirmed the presence ofGAGs and Type I collagen in pellets produced from placental stem cells.No Type II collagen could be found in the pellets by ELISA, but lowlevels of Type II collagen gene expression were found. Further, geneexpression data confirmed the up-regulation of a number of chondrogenicmarkers in induced Placental stem cell pellets compared to uninducedpellets (Table 5)

TABLE 5 Gene Up-regulation Aggrecan 1 + Bone morphogeneic protein 2 ++Cartilage oligo matrix protein ++++ Cartilage-derived ret. acid sens +Collagen, type II + Collagen, type IX + Link protein − Matrilin 3 +Parathyroid hormone receptor 1 + Transcription factor SOX9 + (Level ofup-regulation: − = no up-regulation, + = 1-10 fold; ++ = 10-100 fold,+++ = 100-1,000 fold; and ++++ = 1,000-10,000 fold)

The potential immunogenicity of undifferentiated and chondrogenicdifferentiated placental stem cells was compared using flow cytometry tostain for the presence of the following immune system molecules: MHCA,B,C; MHC DR,DP,DQ; β-2-microglubulin, and CD86. The lack of expressionof MHC II and CD86 and the positive expression of small amounts of MHCA,B,C and β-2-microglobulin were similar (Table 6) betweenundifferentiated placental stem cells and placental stem cells culturedin under chondrogenic conditions.

TABLE 6 Chondorgenic Undifferentiated Differentiated Placental StentPlacental Stem Marker Cell Expression Cell Expression MHC Class II NoneNone CD 86 None None MHC A, B, C Low Low β-2 Microglobulin Low Low

6.14.4 Characterization of Chondrogenic Differentiation of PlacentalStem Cells In Vitro.

This example provides exemplary methods for achieving Objective 1 as setforth in Section 6.11, above. In this example, dynamic pellet culturesare used to permit lengthened culture duration. This extension permitsassessment of temporal gene expression as well as biochemical andhistological analyses of early and late stage markers of chondrogenesisfor placental stem cells in static as well as dynamic pellet culturesfor up to 56 days.

Placental stem cells are isolated from the post-partum placenta, forexample, according to Example 1, above. Placental stem cells areestablished from disrupted tissue in, for example, a complete mediumcontaining low concentrations of fetal calf serum and limited growthfactors, according to Example 1, above. After reaching 80-85%confluence, placental stem cells are subcultured and/or cryopreserved asdescribed elsewhere herein. Flow cytometry analysis is performed toensure that at least 70% or more of isolated cells, for example,CD200⁺CD105⁺CD73⁺CD34⁻ CD45⁻, e.g., according to the method disclosed inExample 3, above. Functional characterization of placental stem cellsfurther includes a chondrogenic differentiation assay.

6.14.5 Pellet Culture in Static and Dynamic Systems

Chondrogenic differentiation of placental stem cells can be carried outas follows. Placental stem cells are cultured to near confluence,trypsinized, washed 2× in incomplete chondrogenesis media (Cambrex) andresuspended at about 500,000 cells/mL in complete chondrogenic media asdescribed above. Aliquots of 500 μL are pipetted into 15 mLpolypropylene centrifuge tubes and centrifuged (800 rpm, 5 min) toinduce pellet formation. Serum-free chondrogenic complete medium (CCM)consisting of 1 mM sodium pyruvate (Sigma), 0.1 mM ascorbicacid-2-phosphate (Wako), 1×10⁻⁷ M dexamethasone (Sigma), 1% ITS(insulin-transferrin-selenium) (Collaborative Biomedical Products), and10 ng/mL recombinant human TGF-β3 (Oncogene Sciences) dissolved inDMEM-low glucose is added to centrifuge tubes. Some pellets aretransferred to bioreactors (Synthecon, model # RCCS-411) containingserum-free CCM for dynamic culturing. Pellets under static or dynamicculture conditions are incubated at 37° C., 5% CO₂ and medium isexchanged every 2-3 days. At days 7, 14, 28, and 56, pellets are removedfrom culture and processed for gene expression, biochemical, orhistological analysis. Comparisons are made with MSCs grown under staticor dynamic culture condition.

To characterize the differentiated chondrocytes, pellets are washed withHEPES buffered saline without calcium and magnesium and digested with 3mg/ml collagenase type 2, 1 mg/ml hyaluronidase, and 0.25% trypsincitrate at 37° C. After digestion the cells are spun down, resuspendedin 1 ml DPBS buffer, and washed. The amount of cells recovered isdetermined by trypan blue dye cell count. RNA is recovered by lysing thecells with a lysis buffer. RNA is isolated using Qiagen RNEASY® kits andquantified using a Nanodrop spectrophotometer. RT-PCR for chondrogenicgene expression is performed using TAQMAN® gene expression probes.Quantitative gene expression is performed for early stage markers offibromodulin and cartilage oligomeric matrix protein. Mid-stage markersof aggrecan, versican, decorin and biglycan are also examined. Genes fortypes II and X collagens and chondroadherin, which are characteristic ofmature chondrocytes, are also examined.

To further characterize the differentiated chondrocytes, Enzyme-LinkedImmunosorbent Assay (ELISA) assays are used to examine proteinexpression of chondro-differentiated placental stem cells. First, thepellets are solubilized. After obtaining a dry weight, rehydratedpellets are digested using pepsin and pancreatic elastase. The collectedsupernatants are used for Collagen Type II and proteoglycan ELISA.Glycosaminoglycan (GAGs) is measured by a methylene blue dye bindingassay.

The differentiated chondrocytes are also subjected to histologicalanalysis as follows. The pellets are fixed in formalin 10%, dehydratedthrough graded alcohols, and embedded in paraffin. Sections are cut at athickness of 5 m and stained with a stain for glycosaminoglycans (e.g.,Alcian blue and/or Safranin-O, and a stain for collagen, e.g., SiriusRed. Alcian Blue is a copper phthalocyanine basic dye that iswater-soluble and colored blue because of its copper content. When usedin a 3% acetic acid solution (pH 2.5), Alcian Blue stains both sulfatedand carboxylated acid mucopolysaccharides and sulfated and carboxylatedsialomucins. Safranin O in the orthochromatic form stains articularcartilage, mucin and mast cell granules on formalin-fixed, paraffinembedded tissue sections. Proteoglycans stain red, cytoplasm stains graygreen and nuclei stain black. Sirius Red dye can be used todifferentiate different collagen types in tissue sections. Underpolarized light, the fibers seemingly glow with bright colors against ablack background. The color of the fibers depends on their thickness; asthickness increases, the color changes from green to yellow to orange tored. Type I collagen, which tends to form thick collagen fibers composedof closely packed thick fibrils, appears as an intense yellow to redcolor. Type III collagen forms thin fibers, composed of loosely disposedthin fibrils and have weak green birefringence. Thus, the colordisplayed is a result of the thickness of the fiber, as well as thearrangement of the collagen molecules.

Four experimental groups are used in this study; cells are grown ineither standard growth media or in CCM and in static or dynamic culturesystems. The quantitative assays are performed on days 7, 14, and 28,and 56. A sample size, n, of 4 is used for all quantitative biochemicalassays (glycosaminoglycan, Type II collagen, and proteoglycan), geneexpression, and histological analyses. One way and two way ANOVAs areperformed to test for statistical differences between groups at eachtime point and over time, respectively for p<0.05. The Tukey-KramerMethod, p<0.05, is used to perform multiple comparisons between groups.

6.14.6 Optimization of Scaffolds for Stimulating Placental Stem CellChondrogenic Differentiation In Vitro.

This example describes experiments designed to achieve Objective 2, setforth above. In brief, the ability of nanofibrous scaffolds to promoteplacental stem cell differentiation into chondrocytes is tested.Electrospun nanofibrous scaffolds, irrespective of composition, promotemesenchymal stem cell differentiation into chondrocytes in vitro asshown above. The materials to be tested as scaffold substrates includepoly(L-lactic acid) (PLLA), type I collagen and a copolymer ofvinylidene fluoride and trifluoroethylene (PVDF-TrFE). Placental stemcells are loaded onto scaffolds generated from these materials andcultured in both static and dynamic conditions. Quantitative geneexpression, biochemical and histological analyses as well as mechanicaltesting is performed during the study time course.

6.14.6.1 Scaffold Fabrication And Characterization

As described above, the electrospinning apparatus comprises a syringefitted with a needle (16-22 gauge), mounted on a Harvard Syringe PumpModel 901. The syringe is filled with the polymer solution. The positiveoutput lead of a high voltage power supply (Gamma High Voltage PowerSupply ES30P) is attached to the needle. The collector is a stainlesssteel plate of dimensions 25×30 cm, which is electrically grounded. Theelectrospinning process is affected by varying the flow rate, solutionconcentration, and the diameter of the needle. The voltage applied tothe solution is 20 kV, and the collector to needle distance is 20 cm.Scaffolds are collected as nonwoven mats at the collector. Thesescaffolds/mats are made of fibers having diameters of approximately200-400 nm.

6.14.6.2 Polymer Solutions for Scaffold Preparation

Initial scaffolds are electrospun from solutions of a Poly L-lactic acid(Alkermes Inc., Medisorb Polymer 75/25 DL High IV) in methylenechloride. Similar scaffolds of Type I collagen (derived from bovinetendon) are produced by dissolving collagen in trifluoroacetic acid(TFA). The piezoelectric polymer, p(VDF-TrFE) is spun from a 10%solution of the polymer in methyl ethyl ketone, as previouslydemonstrated. See Sachlos and Czernuszka, 2003, Eur. Cells Mater.5:29-40.

6.14.6.3 Scaffold Characterization

All scaffolds are examined by the following protocol. Scaffolds areimaged by polarized light optical microscopy and scanning electronmicroscopy. Image analysis techniques are utilized to determine averagefiber diameter and coefficient of variation, as well as the areadistribution between fibers. The fiber parameters of average array porevolume and pore size are by mercury porosimetry. Internal scaffoldstructure is monitored by a variety of thermal analysis techniquesincluding DSC, TGA, DMA, TMA and TSC as appropriate.

For the p(VDF-TrFE) scaffold, a scan of current vs. an applied E fieldwith a Sawyer-Tower circuit is used to identify the propertiesindicative of the polarizability of the p(VDF-TrFE) material. Theseproperties include remnant and saturation polarizability, and thecoercive field (the E field at which polarity switching occurs). Theseproperties have well known values for p(VDF-TrFE) materials. The smallcurrents injected or released by a vibrating electroded electrospunp(VDF-TrFE) mat can also be measured with an electrometer. Thermaldischarge current (TSC) instrumentation is for these studies. Electrodedp(VDF-TrFE) films undergo 1-10% strains in length, width and thicknesswhen subjected to high magnitude (10-100 MV/m), periodic E fields. Thestrains result as the dimensions of the ferroelectric crystallitecontent responds to applied field. It can be expected that electrodedelectrospun p(VDF-TrFE) mats will undergo similar strains.

6.14.6.4 Scaffold Seeding and Differentiation Protocol

Chondrogenic differentiation of placental stem cells is carried outusing media as described above, and elsewhere herein (see, e.g., Section5.4.5, above). All scaffolds are vacuum loaded with about 200,000 cellsusing conventional techniques. See, e.g., Dennis et al., 1998,Biomaterials 19:1323-8. Cell-loaded scaffolds are placed in bioreactors(Synthecon, model # RCCS-4H) containing CCM. The cells are maintained inculture for up to 56 days. Medium is changed every 2-3 days. Comparisonsare made with positive controls, placental stem cells grown withoutscaffolds using standard pellet culture conditions with CCM as describedabove, and with negative controls, and placental stem cells grown withor without scaffolds in the absence of CCM (using standard growthmedia).

6.14.6.5 Quantitative Measurements of Cartilage-Specific ExtracellularMatrix Components and Cell Number

Chondrogenic pellets and cell-laden scaffolds are harvested at 7, 14,28, and 56 days and analyzed for glycosaminoglycan, Type II collagen,and proteoglycan synthesis. These assays allow for rapid, highthroughput screening for cartilage markers using 96-well plate formats.To do so, the samples are washed with phosphate buffered saline anddigested with 200 μL papain solution (1 μg/mL in 50 mM sodium phosphatepH 6.5, containing 2 mM N-acetyl cysteine and 2 mM EDTA) for 16 hours at65° C. Glycosaminoglycan and proteoglycan synthesis are measuredquantitatively using an ELISA kit (BLYSCAN™ Kit, Accurate Chemical andScientific Corporation, Westbury, N.Y.). Type II collagen synthesis ismeasured by an ELISA kit (Arthrogen-CIA, Chondrex, Inc.). Cell number isquantified by DNA measurement, using pico-green fluorescence assay(Molecular Probes, Inc.).

6.14.6.6 Tissue Morphology by Histological Analysis

Histological staining and viewing at days 21 and 35 is used tocharacterize cell and tissue morphology of the chondrogenic scaffolds.Cell pellets and cell-laden scaffolds are harvested and fixed in 10%buffered formalin for 2 hours at room temperature. Pellet and scaffoldsare dehydrated by treatment with a series of graded alcohols, cleared bytreatment with xylene and xylene substitute, and infiltrated withparaffin. Thin sections are slide-mounted and stained with toluidineblue and safranin O.

6.14.6.7 Analysis of mRNA Changes From Differentiation

As described previously for pellet cultures, samples are washed withHEPES buffered saline without calcium and magnesium and digested with 3mgs/ml collagenase type 2, 1 mg/ml hyaluronidase, and 0.25% trypsincitrate at 37° C. After digestion the cells are spun down, resuspendedin 1 mL DPBS (Dulbecco's Phosphate-Buffered Saline) buffer, and washed.The amount of cells recovered is determined by trypan blue dye cellcount. RNA is recovered by lysing the cells with a lysis buffer. RNA isisolated using Qiagen RNEASY® kits and quantified using Nanodrop. RT-PCRfor chondrogenic gene expression is accomplished using TAQMAN® geneexpression probes from ABI. Quantitative gene expression is performedfor early stage markers of fibromodulin and cartilage oligomeric matrixprotein. Mid-stage markers of aggrecan, versican, decorin and biglycanare also examined. Genes for types II and X collagens andchondroadherin, which are characteristic of mature chondrocytes, arealso examined.

6.14.6.8 Number of Groups and Statistical Analyses

Six experimental groups are used in this study: three materialcompositions (PLLA, Type I Collagen, and pVDF-TrFE), and cells are grownin either standard growth media or in CCM. The quantitative assays areperformed on days 7, 14, 21, and 28 days. A sample size, n, of 4 is usedfor all quantitative assays (glycosaminoglycan, Type II collagen, andproteoglycan). One way and two way ANOVAs are performed to test forstatistical differences between groups at each time point and over time,respectively for p<0.05. The Tukey-Kramer Method, p<0.05, is used toperform multiple comparisons between groups.

6.14.7 Evaluation of In Vivo Repair of Osteochondral Defects in a RabbitModel Using Placental Stem Cell-Scaffold Constructs.

This Example describes experiments designed to achieve Objective 3, setforth above. Briefly, scaffolds identified as supporting chondrogenicdifferentiation are evaluated in combination with placental stem cellsin the repair of osteochondral defects in rabbits.

6.14.7.1 Animal Model

A rabbit, partial-weight bearing articular cartilage repair model isemployed to study the chondrogenic effects of cell/scaffold constructs.Depending upon the number of scaffolds that support placental stem cellchondrogenesis, the number of rabbits is determined. Rabbits, NewZealand strain, are randomly assigned to the groups. An n of 4 per groupis implanted. Average animal weight is between 3-5 kg and animals arespecific pathogen free (SPF).

A 3.5 mm cylindrical defect is created in the intercondylar groove ofthe distal femur of each animal, and a cylindrical, cell/scaffoldconstruct is implanted into the defect in a press-fit fashion. Thecontralateral knee of each rabbit serves as an internal control. Thesame defect is created and a scaffold of the same composition andarchitecture without cells is inserted. The knee to act as internalcontrol is randomized by picking an opaque envelope, prior to theprocedure, that states left or right as the control knee.

To implant the scaffolds, intravenous pentobarbital (45 mg/kg) isadministered to initiate anesthesia. Anesthesia is maintained throughinhalation of 0.5-2% isoflurane delivered in oxygen. The rabbit isplaced in the supine position and each knee is shaved and prepped in asterile fashion with a 70% alcohol scrub over the incision site. Thesurgical site is isolated with sterile drapes.

A lateral parapatellar incision and arthrotomy is performed. The femoralcondyles are exposed by medial dislocation of the patella. A 3.5 mmdrill bit is used to create the defect in the intercondylar groove ofthe distal femur. Defect depth is 3-5 mm in depth. The scaffold with orwithout cells is sutured into the defect utilizing a small absorbablesuture material (6-0/7-0 vicryl). The wound is then closed in layerswith absorbable sutures. The same procedure is performed on thecontralateral knee as outlined above to serve as an internal control.

Post-operation, all animals are allowed weight-bearing as tolerated intheir cages. Buprenorphine 0.03 mg/kg is administered every 12 hourssubcutaneously for post-operative pain control for the first 5-7 dayspost-operatively. Regular diet is provided.

Rabbits are euthanized utilizing a lethal dose of pentobarbital at 12weeks post-operatively. The distal femora of each rabbit are harvested.Gross evaluation of the repair site is documented for color andappearance compared to the normal surrounding tissue; evidence of jointarthrosis is documented as well. Specimens (n=4 per group) aredecalcified and paraffin embedded for histological evaluation andstaining. Histological evaluation is graded utilizing a modifiedO'Driscoll score. N=8 specimens per group are used for mechanicaltesting. Compression testing is performed based on previously reportedprotocols for nanofibrous scaffolds.

6.15 Example 15: Identification of a CD34⁺CD45⁻ Cell Population inPlacental Perfusate

The purpose of this study was to phenotypically characterize and comparecells from matched placenta perfusate (HPP) and cord blood (HUCB) units(n=10) and to identify additional useful cell surface markers forplacenta perfusate using multi-parameter flow cytometry. To assess thequality of the cells, total nucleated cells (TNCs) and cell viabilitywere also measured. Since post-thaw samples are close to the conditionof cells prior to their use in preclinical or clinical studies,characterization of the placenta perfusate focused on these samples. Forcomparison purposes, a donor matched cord blood for each placenta unitwas tested. Including matched HUCB units in this project allowedevaluation of the differences between cell populations in the placentaperfusate and umbilical cord blood collected from the same donor.

Materials and methods: Placental perfusates were obtained from perfusionof placentas from normal births using 0.9% NaCl. Matched units ofumbilical cord blood were collected and cryopreserved by standardmethods, and thawed immediately prior to use. Frozen HPP and HUCBsamples were drawn from a liquid nitrogen tank and thawed in a 37° C.water bath immediately. Cells were assessed by flow cytometry, bywashing the cells in PBS with 2% fetal calf serum, staining withconjugated antibodies, and analyzing using either a BD FacsCalibur or aBD ARIA (Becton Dickinson, San Jose, Calif.). Antibodies used includedPE-CD34 (BD Cat #348057) and PerCP-CD45 (BD Cat #340665). Cell sortingexperiments were performed after staining with the appropriateantibodies and cells were placed in a standard CFU assay system usingMethoCult.

Results: Flow cytometry determined that a cell having a CD34⁺CD45⁻phenotype was 4-fold enriched in HPP as compared to HUCB (FIG. 10). Datain Table 7 was derived from HPP and HUCB cells that were sorted usingthe FACS ARIA cell sorted for Becton Dickinson. Placental perfusate stemcells were sorted based on the following phenotypes: CD34⁻ CD45⁻,CD34⁺CD45⁻ and CD34⁺CD45⁺. The double negative cell type was notexpected to produce any CFU and served as a sort purity control. TheCD34⁺CD45⁺ cell type is the classical CB stem cell and served as thepositive control for the sort and the CFU assay. The test phenotype ofCD34⁺CD45⁻ was not present in sufficient quantities in the HUCB to allowfor sorting and CFU, but from HPP cells were obtained. As seen in Table1, cells from HPP gave rise to larger numbers of CFU-E and BFU-E, aswell as providing the same CFU pattern as found in HUCB. In addition,the HPP CD34⁺CD45⁺ cells provided CFU-GEMM, a population not detected inHUCB nor produced by CD34⁺CD45⁺ cells in HUCB.

TABLE 7 CFU DATA Chart CD34−; CD45− Cells CFU-E/BFU-E CFU-GM CFU-GEMM1000 cells/ 3000 cells/ 9000 cells/ 1000 cells/ 3000 cells/ 9000 cells/1000 cells/ 1000 cells/ 9000 cells/ Unit # well well well well well wellwell well well 327950HPP 0 0 0 0 0 0 0 0 0 327940CB 0 0 0 2 2 0 0 0 0CD34+; CD45− Cells CFU-E/BFU-E CFU-GM CFU-GEMM 50 cells/ 150 cells/ 450cells/ 1000 cells/ 50 cells/ 150 cells/ 450 cells/ 1000 cells/ 50 cells/150 cells/ 450 cells/ 1000 cells/ well well well well well well wellwell well well well well 327950HPP 0 2 0 1 0 0 0 1 0 0 0 0 327940CB N/AN/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A CD34+; CD45+ CellsCFU-E/BFU-E CFU-GM CFU-GEMM 50 cells/ 150 cells/ 450 cells/ 50 cells/150 cells/ 450 cells/ 50 cells/ 150 cells/ 450 cells/ well well wellwell well well well well well 327950HPP 1 4 7 4 4 5 0 0 0 327940CB 0 0 I5 12 0 0 0 0 Duplicate wells CD34−; CD45− Cells CFU-E/BFU-E CFU-GMCFU-GEMM 1000 cells/ 3000 cells/ 9000 cells/ 1000 cells/ 3000 cells/9000 cells/ 1000 cells/ 1000 cells/ 9000 cells/ well well well well wellwell well well well 327950HPP 0 0 0 0 0 0 0 0 0 327940CB 0 0 0 0 1 0 0 00 CD34+; CD45− Cells CFU-E/BFU-E CFU-GM CFU-GEMM 50 cells/ 150 cells/450 cells/ 1000 cells/ 50 cells/ 150 cells/ 450 cells/ 1000 cells/ 50cells/ 150 cells/ 450 cells/ 1000 cells/ well well well well well wellwell well well well well well 327950HPP 0 1 2 1 0 0 1 0 0 0 0 0 327940CBN/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A CD34+; CD45+ CeltsCFU-E/BFU-E CFU-GM CFU-GEMM 50 cells/ 150 cells/ 450 cells/ 50 cells/150 cells/ 450 cells/ 50 cells/ 150 cells/ 450 cells/ well well wellwell well well well well well 327950HPP 3 2 8 2 2 14 0 0 0 327940CB 0 00 16 14 0 0 0 0 HPP: human placental perfusate CB: Cord bloodCFU-E/BFU-E: colony forming unit, erythrocyte/blast forming uniterythrocyte CFU-GM: colony forming unit, granulocyte macrophageCFU-GEMM: colony forming unit, granulocyte, erythrocyte, monocyte,megakaryocyte

In another study, CD34, CD45, CD31 and CDH5 gene expression levels werecompared in CD34⁺CD45⁺ and CD34⁺CD45⁺ cell populations isolated from thesame placental perfusate (HPP).

Materials and Methods:

CD34 CD45⁻ and CD34⁺CD45⁺ cell populations were obtained as describedabove with cell purity greater than 90%, and subjected to RNApreparation using RNAQUEOUS®-4PCR Kit (Ambion, Cat # AM1914). In brief,the isolated cells (5×10⁵ cells) were lysed in the guanidinium lysissolution. The sample lysate was then mixed with an ethanol solution, andapplied to a silica-based filter which selectively and quantitativelybinds mRNA and the larger ribosomal RNAs. Very small RNAs such as tRNAand 5S ribosomal RNA were not quantitatively bound. The filter was thenwashed to remove residual DNA, protein, and other contaminants, and theRNA was eluted in nuclease-free water containing a trace amount of EDTAto chelate heavy metals. The silica filter was housed in a smallcartridge which fits into the RNase-free microfuge tubes supplied withthe kit. The sample lysate, wash solutions, and elution solution weremoved through the filter by centrifugation or vacuum pressure. Afterelution from the filter the RNA was treated with the ultra-pure DNase 1provided with the kit to remove trace amounts of DNA. Finally, the DNaseand divalent cations were removed by a reagent also provided with thekit. The concentration and purity of the recovered RNA was determined bymeasuring its absorbance at 260 and 280 nm. The RNA can then be used forcDNA synthesis using TAQMAN® Reverse Transcription Reagents (AppliedBiosystems, Cat # N8080234) followed by real-time PCR analysis by 7900HTFast Real-Time PCR System using Taqman Gene Expression Assays of CD34(Applied Biosystems, Cat # Hs00990732_m1), CD45 (Applied Biosystems, Cat# Hs00236304_m1), CD31 (Applied Biosystems, Cat # Hs01065289_m1), andCDH5 (Applied Biosystems, Cat # Hs00174344 ml).

Results:

Real-time PCR analysis determined that CD34 expression in CD34 CD45⁻ andCD34⁺CD45⁺ cells was comparable. As expected, CD45 expression was notdetectable in CD34⁺CD45⁻ cells, but was, however, detectable inCD34⁺CD45⁺ cells. CD31 expression in CD34⁺CD45⁺ cells was 0.05% of thatin CD34⁺CD45⁻ cells. CDH5 expression in CD34⁺CD45⁺ cells was 13.66% ofthat in CD34⁺CD45⁻ cells.

6.16 Example 16: Enrichment of CD34⁺ Cells from Human Placenta Perfusate

This example describes the enrichment of CD34⁺ cells from human placentausing magnetic antibody-coated-bead separation (MACS).

A cell suspension from human placental perfusate is obtained andresuspended in MACS buffer (PBS pH 7.2, +0.5% BSA+2 mmol EDTA)containing ACD (anticoagulant citrate dextrose). An aliquot is collectedfor a first flow sample. 6 mL of Ficoll is added to a separate 15 mLtube, and the cell suspension is layered over Ficoll very slowly. Thecell suspension in Ficoll is centrifuged at 300×g (avg.) for 35 minutes,20° C., no brake in a Beckman coulter Allegra X12R Centrifuge with aSC4750 rotor. Upon completion of centrifugation, the supernatant isaspirated carefully, and the mononuclear cells settled at the interfaceare collected into a separate tube. This material is resuspended to atotal volume of 10 mL with MACS buffer containing ACD. An aliquot iscollected for a second flow sample. Cells are counted and checked forviability. The cells are then centrifuged at 400×g (avg.) in an SC4750rotor for 15 minutes at 4° C. When centrifugation is completed, thesupernatant is aspirated, and the cells are resuspended to 100 μL inMACS buffer containing ACD. STEMSEP™ selection cocktail (StemCellTechnologies, Inc., Vancouver, BC Canada) is added at a concentration of100 μL/1 mL of cells (at concentration of 1 μL/2×10⁶ cells). The cellsand cocktail are mixed well and incubated for 10 minutes at 4-8° C.Magnetic colloid is added at 60 μL/1 mL of cells (at concentration of 1μL/3.33×10⁶ cells). The cells and colloid are mixed well and incubatedfor 10 minutes at 4-8° C. A 10× volume of refrigerated MACS buffercontaining ACD is then added to the cells, and the resulting solution iscentrifuged at 400×g (avg.) in an SC4750 rotor for 8 minutes at roomtemperature. The supernatant is aspirated, and the cells are resuspendedin 2 mL of MACS buffer containing ACD. The suspension is optionallyfiltered at this point. A third aliquot is collected for a flow sample.Cells are then analyzed on an AUTOMACS™ automated magnetic cell sorter(Miltenyi Biotec) using program POSSELD2, placing collection tubes atpositions “POS 2” and “NEG1”. About 2 mL of positively selected cellsare collected. The cell suspension is then washed and centrifuged at400×g (SC4750 rotor) for 10 minutes at room temperature and resuspendedto 1 mL in PBS containing 1% FBS.

6.17 Example 17: In Vitro Colony Forming Unit Assay

Total nucleated cells are isolated from a unit of cord blood byHetastarch separation. Total nucleated placental cells are obtained from750 milliliters of placental perfusate by Ficoll separation. The totalnucleated cells from placenta and cord blood are combined in triplicatein 35 mm culture dishes in Methocult GF+H4435 medium (Stem CellTechnologies, Vancouver, Canada), or RPMI 1640 medium supplemented with2% fetal calf serum and 1% Stemspan CC 100 cytokine cocktail (Stem CellTechnologies, Vancouver, Canada). Cells are combined in at least tworatios (e.g., 2×10⁵:2×10⁵; 1×10⁵:3×10⁵; 3×10⁵:1×10⁵), and are culturedfor 14 days. The morphology of the cells is then examined under phasecontrast microscope, and the total number of colony-forming units (e.g.,CFU-GM, CFU-L, CFU-M, CFU-G, CFU-DC, CFU-GEMM, CFU-E) are recorded. Adetermination is then made as to which ratio produces the highest numberof colony-forming units.

EQUIVALENTS

The present invention is not to be limited in scope by the specificembodiments described herein. Indeed, various modifications of theinvention in addition to those described will become apparent to thoseskilled in the art from the foregoing description and accompanyingfigures. Such modifications are intended to fall within the scope of theappended claims.

Various publications, patents and patent applications are cited herein,the disclosures of which are incorporated by reference in theirentireties.

What is claimed is:
 1. A method of producing a hepatocyte, comprisingcontacting a CD10⁺, CD34⁻, CD105⁺ and CD200⁺ placental stem cell withsodium butyrate under conditions and for a time sufficient for said stemcell to exhibit a characteristic of a hepatocyte.
 2. The method of claim1, wherein said characteristic is production of asialogylcoproteinreceptor, alpha-1-antitrypsin, albumin, cytochrome P450 activity, or theincreased production of cytokeratin 18 relative to an undifferentiatedplacental stem cell.
 3. The method of claim 1, wherein said culturingcomprises encapsulating said stem sell in alginate-poly-L-lysine.
 4. Ahepatocyte or hepatocytic cell produced by the method of claim
 1. 5. Amethod of treating a subject having a disease, disorder or conditionassociated with liver inflammation, comprising introducing thehepatocyte or hepatocytic cell of claim 4 to said subject.
 6. The methodof claim 5, wherein said disease, disorder or condition is cirrhosis orviral infection.
 7. A mouse comprising human placental stem cell-derivedhepatocytes or hepatogenic cells, wherein said mouse is produced by amethod comprising the steps of: a. irradiating said mouse with gammaradiation sufficient to kill substantially all of the endogenous bonemarrow cells; b. administering to said mouse sufficient bone marrow orbone marrow-derived cells from a NOD/SCID mouse to reconstitute thehematopoietic system of the mouse; and c. transplanting to said mouse aplurality of hepatocytes or hepatogenic cells, wherein said hepatocytesor hepatogenic cells are differentiated from a plurality of CD10⁺,CD34⁻, CD105⁺, CD200⁺ placental stem cells.
 8. The mouse of claim 7,wherein said placental stem cell is additionally cytokeratin 18⁺.
 9. Themouse of claim 7, wherein said hepatocytes or hepatogenic cells areadministered into an ear pinna of the mouse.
 10. The mouse of claim 8,wherein said hepatocytes or hepatogenic cells are infected with a virus.11. The mouse of claim 10, wherein said virus is hepatitis A virus,hepatitis B virus, hepatitis C virus, hepatitis D virus, or hepatitis Evirus.
 12. A method of identifying an antiviral agent, comprisingcontacting the mouse of claim 12 with a compound of interest, whereinserum from said mouse has detectable levels of virus, and wherein saidcompound is an antiviral agent if said contacting results in adetectable reduction in the amount of said virus in serum from saidmouse, compared to serum from said mouse not contacted with the compoundof interest.
 13. The method of claim 12, wherein said virus is hepatitisA virus, hepatitis B virus, hepatitis C virus, hepatitis D virus, orhepatitis E virus.
 14. The method of claim 13, wherein an antigen ofsaid virus is detected.
 15. The method of claim 13, wherein a nucleicacid of said virus is detected.
 16. The method of claim 14, wherein saidvirus is hepatitis B virus.
 17. The method of claim 14, wherein saidantigen is HBeAg or HBsAg.
 18. A composition comprising a plurality ofcells encapsulated in alginate, wherein said cells are differentiatedfrom placental stem cells, and wherein said cells express at least onemarker of a hepatocyte not expressed by, or expressed to a detectablydifferent degree than, an adherent placental stem cell that is CD10⁺,CD34⁻, CD105⁺ and CD200⁺.
 19. The composition of claim 18, wherein saidalginate is in the form of beads.
 20. The composition of claim 19,wherein said beads are from about 200 μm to about 800 μm in size. 21.The composition of claim 19, wherein said beads average about 500 μm insize.
 22. A composition comprising isolated adherent CD10⁺, CD34⁻,CD105⁺, CD200⁺ placental stem cells and an electrospun nanofibrousscaffold.
 23. The composition of claim 22, wherein said nanofibrousscaffold comprises fibers of poly(L-lactic acid) (PLLA), poly lacticglycolic acid (PLGA), type I collagen, a copolymer of vinylidenefluoride and trifluoroethylnee (PVDF-TrFE), poly(-caprolactone),poly(L-lactide-co-ε-caprolactone) [P(LLA-CL)] (e.g., 75:25), and/or acopolymer of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) andtype I collagen.
 24. The composition of claim 22, wherein saidnanofibrous scaffold comprises fibers that average between about 250nanometers and about 10 μm in thickness.
 25. The composition of claim22, wherein said composition is contacted with conditions in which theplacental stem cells differentiate into chondrogenic cells orchondrocytes.
 26. A method of making a composition comprising contactingadherent CD10⁺, CD34⁻, CD105⁺, CD200⁺ placental stem cells with anelectrospun nanofibrous scaffold, wherein said nanofibrous scaffold ismade by electrospinning PLLA or PLGA at about 20 kV at about 30 cmneedle to collector distance and about 0.05 mL/min. to about 0.1 mL/minflow rate, wherein said PLLA or PLGA are in solution at about 10% w/w toabout 20% w/w.
 27. An isolated cell population enriched for CD34⁺, CD45⁻placental stem cells.
 28. The cell population of claim 22, wherein atleast 50% of cells in said population are CD34⁺ and CD45⁻.
 29. The cellpopulation of claim 22, wherein at least 70% of cells in said populationare CD34⁺ and CD45⁻.
 30. The cell population of claim 27, wherein atleast 90% of cells in said population are CD34⁺ and CD45⁻.
 31. The cellpopulation of claim 27, wherein said population comprises a stem cellthat is not CD34⁺ and CD45⁻.
 32. The cell population of claim 31,wherein said stem cell that is not CD34⁺ and CD45⁻ is a CD34⁻ adherentplacental stem cell.
 33. The cell population of claim 32, wherein saidadherent placental stem cell is CD200⁺, CD105⁺, CD90⁺, CD10⁺, CD34 andCD45⁻.
 34. The cell population of claim 31, wherein said stem cell thatis not CD34⁺ and CD45⁻ is a bone marrow-derived mesenchymal stem cell.35. The cell population of claim 31, wherein said stem cell that is notCD34⁺ and CD45⁻ is a CD34⁺, CD45⁺ hematopoietic stem cell.
 36. The cellpopulation of claim 8, wherein said stem cell that is not CD34⁺ andCD45⁻ is contained within cord blood or placental blood.
 37. A method ofproducing a CD34⁺, CD45⁻ placental stem cell population, comprisingselecting CD34⁺ cells from a population of placental cells to form apopulation of CD34⁺ placental cells, and removing from said populationof CD34⁺ placental cells CD45⁺ cells, wherein a CD34⁺, CD45⁻ placentalstem cell population is produced.